:A A L Carburetor9D-5

March 198 1Supersedes 9D-5

Dated May 1973Models 4MV-4MC-M4ME-M4M CService Manual

Delco

IMPORTANT SAFETY NOTIC E

Proper service and repair is important to the safe, reliable operation of all motor vehicles .The procedures recommended by Rochester Products Division of General Motors an ddescribed in this service manual are effective methods of performing service operations .Some of these service operations require the use of tools specially designed for the purpose .The special tools should be used when and as recommended .

It is important to note that this manual contains various CAUTIONS and NOTICES whic hshould be carefully read in order to minimize the risk of personal injury to service personne lor the possibility that improper service methods will be followed which may damage th evehicle or render it unsafe . It is also important to understand that these Cautions an dNotices are not exhaustive . Rochester Products could not possibly know, evaluate an dadvise the service trade of all conceivable ways in which service might be done or of th epossible hazardous consequences of each way . Consequently, Rochester Products has no tundertaken any such broad evaluation . Accordingly, anyone who uses a service procedur eor tool which is not recommended by Rochester Products must first satisfy himsel fthoroughly that neither his safety nor vehicle safety will be jeopardized by the servic emethod he selects .

All information, illustrations, and specifications contained in this manual are based on th elatest product information available at time of publication approval . The right is reserved t omake changes at any time without notice .

CONTENTSGENERAL DESCRIPTION 3

OPERATING SYSTEMS 4

MAJOR SERVICE OPERATIONS 26

NOTE: USE THIS MANUAL PLUS SECTIONS 9D-5A & 9D-5S FOR COMPLETE SERVIC EINSTRUCTIONS.

©1981 GENERAL MOTORS CORPORATIO NPRINTED IN U .S.A.

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TYPICAL MODELS-4MV-M4M E

Figure 1 Model 4MV Figure 2 Model M4M E

GENERAL DESCRIPTIONThe Rochester Quadrajet is a four barrel, two stage

carburetor of down draft design . It has been proven tobe dependable and a versatile performer as witnessed byits broad application and usage since its first introduc-tion in 1965 . Modern demands for greater fuel economyand improved emission control have resulted in signifi-cant refinement of the original design . The RochesterQuadrajet has evolved to the point of being an efficien tand sophisticated fuel control device that is right fo rthe times and yet maintains the serviceability that is s oimportant to those responsible for vehicle performanc eand customer satisfaction .

The Quadrajet carburetor has two distinct and sepa-rate design stages. Each stage operates to provide ablend of economical operation and responsive engineperformance .

The primary side of the carburetor (fuel inlet side )has two small bores. Each bore contains a triple ven-turi arrangement equipped with plain tube nozzles . Thetriple venturi provides excellent fuel atomization an ddelivery in the off idle and part throttle ranges of engineoperation .

Fuel metering is controlled through the usage oftapered primary metering rods that are suspended withi nfinely machined metering jets . The metering rods aremoved vertically by engine vacuum control . This is accom -plished by the use of a spring-loaded piston and rodhanger assembly and results in the control of fuel allowe dto pass through the metering jets and to the engin eduring low speed and moderate speed operation .

Some models use multiple stage enrichment method sthat may incorporate additional rods, jets and/or powerpiston arrangements . There are models that have device sthat respond to changes in atmospheric pressure as well .The objective is to provide a high degree of sensitivit yto air/fuel mixture control at lower and midrange engin espeeds . The primary side of the Quadrajet carburetor

has the design features to meet these needs . The indi-vidual systems are described in detail later in sections o fthis text .

The secondary side of the Quadrajet has two largerbores . This increased area, when combined with that o fthe primary side of the carburetor, provides an air de -livery capacity that can satisfy a broad range of engin eoperating conditions .

An air valve, positioned above the secondary bores ,controls the fuel delivery for high demand conditions .This secondary air valve is connected mechanically to apair of secondary metering rods that are tapered and ar esuspended within a pair of fuel metering orifices . Thefuel passing through these secondary orifices is directedto a set of delivery nozzles located at the top of each secon -dary bore and below the air valve . The fuel flowthrough the nozzles is thereby controlled in direct pro -portion to air flowing through the secondary bores .

There are two basic carburetor model designs :

First released in 1965, the 4MV is an automatic chok emodel designed for use with a manifold mounted thermo-static choke coil . The 4MC model also is an automaticchoke carburetor but with the choke thermostatic coi llocated in a choke housing mounted on the side of th efloat bowl . Except for choke systems, all models hav ebasically the same principles of operation (Figure 1) .

First released in 1975, the M4ME models differ fromthe conventional 4MV-4MC carburetor models in tha tthe "M" prefix designates "modified", indicating th eprimary side is revised to accomodate an adjustabl emetering rod assembly with filler spool, or aneroid -metering rod assembly, where required, and the auxiliar ypower piston assembly (if used). The aneroid feature isnormally used to achieve altitude compensation in air /fuel mixtures (designated Models M4MCA-M4MEA )(Figure 2) .

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Later "modified " models use separated main well swith an aneroid cavity insert in the float bowl replacingthe adjustable metering rod or aneroid-metering rodassembly .

On all models, the fuel chamber is centrally locate dto avoid problems of fuel spillage causing engine tur ncut-out and delayed fuel flow to the carburetor bores .The fuel chamber is relatively small in volume to reduc efuel evaporation during hot engine "shutdown". A plasticbowl insert is included to reduce the free volume abov ethe fuel level to prevent fuel loss to the main meteringjets during critical vehicle maneuvers .

The float system has a single pontoon float and fue linlet valve for simplification and ease of servicing . Anintegral fuel filter (or strainer), and check valve (if used) ,located in the float bowl ahead of the fuel inlet valve, iseasily removed for cleaning or replacement .

All models have an Adjustable Part Throttle (A .P.T. )screw located either in the throttle body (since 1968 o n4MV-4MC models) or in the float bowl ( "M" modifiedmodels) to aid in refinement of fuel mixtures for goo demission control .

The thermostatic choke coil assembly on 4MV model sis heated by hot exhaust gases that flow through a specia lpassage in the intake manifold . On 4MC-M4MC-an dM4MCA models, the thermostatic coil assembly i swarmed by exhaust heated air supplied through a tub eto the choke housing mounted on the float bowl . M4MEand M4MEA models use an electrically heated thermo-static coil assembly to control choke mixtures afte rengine start and cold driveaway .

The throttle body is aluminum to reduce overall weigh tand to improve heat distribution, plus there is a thickthrottle body to bowl insulator gasket to keep excessiveheat from the float bowl causing fuel percolation.

Some Quadrajet applications use a shim between th ethrottle body and flange gasket . The shim is used t oprotect the carburetor aluminum throttle body from ex-haust gases flowing through the heat cross-over orexhaust gas recirculation passage in the intake manifold .

CARBURETOR IDENTIFICATIO NEarly Quadrajet carburetors (Figure 3) have the

model number identification stamped on a circular ta gpressed into a recess on the float bowl casting in a fla tarea on the throttle lever side . Later model Quadrajet

Figure 3 Carburetor Identification Tag - EarlyModels

carburetors have no tag but include the part numberstamped vertically on the left rear corner of the floa tbowl casting adjacent to the secondary pick-up lever(Figure 4) . If replacing the float bowl, follow the manu-facturer 's instructions contained in the service packag eso that the identification number can be transferred t othe new float bowl . Refer to the part number on th ebowl when servicing the carburetor .

Figure 4 Carburetor Identification Location -Late Model s

SERVICE FEATURESThe primary side of the carburetor has six operatin g

systems . They are float, idle, main metering, power ,pump, and choke. All systems receive fuel from one fue lchamber .

The following text covers the operating systems fo rease in trouble-shooting and also recommended serviceprocedures . There are some design variations betweendifferent models which will be covered in that part ofthe text pertaining to that particular system or serviceprocedure .

OPERATING SYSTEMSFLOAT SYSTEM

The Quadrajet carburetor has a centrally located fue lchamber in the float bowl (Figure 5) . The fuel chamberis centered between the carburetor bores to assure anadequate fuel supply to all metering systems with respec tto car inclination or severity of turns .

The float system (Figures 6 or 7) consists of a fuelchamber, fuel filter (with check valve on M4MC-M4M Eapplications) or a fuel inlet strainer (some 4MV appli-cations), a single closed-cell plastic float pontoon wit hintegral float lever, a float hinge pin, float valve an dpull-clip, float valve seat (with or without "windows ") ,and internal vents . Also, some applications include eitheran idle vent valve, vacuum vent switch valve, or externa l

CARBURETOR

CARBURETORMODEL N O

CHANGELETTER

A AT( I5/MO B Y RBUILT (JAN 1967 )

MODELS 0,2G .4G MODELS M 4M(EARLY)

NOPEGOIONSTAMP

SHIF T(DENT.

MODEL NO.

CARBURETOR IDENTIFICATIO N"4M" TYPE

ASSEM .PLANT COD E

YEAR

DAY OF YEAR

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March 198 1

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Figure 5 Centralized Fuel Chambe r

Figure 6 Float System 4MV-4MC

Figure 7 Float System M4MC-M4ME

vent connector tube leading to the vapor canister, tovent excessive fuel vapors that form in the fuel chambe rabove the fuel surface that could disrupt hot engin eoperation . A plastic filler block is located in the top o fthe fuel chamber over the float valve to prevent fuelslosh in this area. On M4MC and M4ME models, eithera filler spool or an aneroid cavity insert is used in thefuel chamber to reduce fuel slosh on turns . Also, ametal baffle is added to the pump well fill slot in th efloat bowl of M4MC-M4ME models to reduce fuel slos hduring various vehicle maneuvers .

On most models, an integral 1-inch or 2-inch pleate dpaper fuel inlet filter, dependent upon model, is mounte din the front of the float bowl behind the fuel inlet nu tto filter impurities from the incoming fuel . If used, acheck valve is pressed into the neck of the fuel filter .The check valve consists of a plastic disc contained in aplastic retainer. It is held in the normally closed positionby a small spring which exerts pressure on the checkvalve . When the engine starts and fuel flow pressure fro mthe fuel pump enters the inlet nut, it pushes the smal lcheck valve off its seat . Fuel flows past the valve int othe inside of the filter and continues on through the filte rto the float valve and seat . With the engine off, thecheck valve closes and shuts off fuel flow to the carbu-retor to prevent fuel leaks if a vehicle roll-over shouldoccur .

The check valve retainer also has a flanged nec kwhich seals between the filter and fuel inlet nut .

NOTICE : If used, the check valve must b einstalled to meet government safety standard sfor roll-over . New service replacement filtersinclude the check valve where required .

The fuel filter is held in position by the force of aspring located between the filter assembly and the fuelinlet nut cavity .

NOTICE : It is very important that the filterbe serviced according to recommended main-tenance intervals to prevent dirt and othe rimpurities from entering the carbureto rmetering orifices .

The float system operates in the following manner :

Fuel flow from the fuel pump enters the carburetorfuel inlet nut . It opens the check valve (if used) in th efilter against spring force and flows through the filterelement (or strainer), and then passes from the filterchamber up through the float valve seat and flows pastthe float valve on into the fuel chamber . As the in -coming fuel enters the fuel chamber, the float pontoo nrises and forces the float valve closed, shutting off fuelflow at a prescribed level . As fuel is used from the fuelchamber, the float pontoon drops to open the float valveallowing fuel to again enter the fuel chamber. Thiscycle continues, maintaining a near constant fuel leve lin the fuel chamber for all ranges of engine operation .

A float pull clip, fastened to the float valve, hooks

EXTERNA LIDLE VEN T

VALV E

FUEL INLE TFILTER

-J

"'CHECKCHECK VALVE

VALVESEAT FLOAT SYSTEM

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March 1981Page 6 F'

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over the edge of the float lever at the center as show nin Figures 6 or 7 . Its purpose is to assist in lifting thefloat valve off its seat whenever fuel level in the fuelchamber is low.

NOTICE: Do not place pull clip throughsmall holes in top of float lever . Severe flood -ing will result .

There are two types of float valves used in the Quadra-jet carburetor : One type is diaphragm assisted and th eother is the conventional needle and brass seat .

The diaphragm assisted float valve (shown in the insetFigure 6) is used primarily with a smaller float and onengines equipped with high pressure fuel pumps . Thevalve seat is a brass insert and is pressed into the bow lfuel inlet channel below the diaphragm needle tip . Theseat is not removable, as the valve tip is of a materia lwhich makes seat wear negligible . Care should be use dduring servicing so that the seat is not nicked, scored ,or moved . The float valve is factory staked and testedand should not be re-staked in the field .

Fuel flow through the diaphragm assisted float valvevaries from the conventional float needle . With the con-ventional type (as shown in Figure 7) fuel flows fro mthe inlet filter and inlet channel up through the needl eseat orifice past the float needle valve and spills overinto the float bowl . With the diaphragm type float valve ,fuel from the inlet filter enters the channel above th efloat valve tip . When fuel level is low in the bowl, th efloat valve is off its seat and fuel flows down past th evalve tip into a fuel channel which leads upward throughthe bowl casting to a point above normal liquid leve land spills over into the float bowl .

The diaphragm type float valve differs in operationfrom the conventional float needle in that a larger sea torifice can be used to provide greater fuel flow to thefloat chamber and yet allow the use of a small float .This is accomplished through a balance of forces actin gon the float valve and diaphragm against fuel pum ppressure . Fuel pressure entering the float valve chambe rtends to force the valve closed . However, the samepressure is also acting on the float valve diaphragm . Thediaphragm has a slightly larger area than the floatvalve head, therefore the greater pressure acting on thediaphragm tends to push the valve off its seat . Theforce of the float arm acting on the valve stem, as thefloat bowl fills, overcomes this pressure difference andcloses the valve . Therefore, the float's function is to over-come the pressure difference and it does not have t oforce a valve closed against direct fuel pump pressur eas does the conventional needle type .

To improve hot engine starting and to prevent roughidle which may'result from excessive fuel vapors tha tmay form in the fuel chamber, various methods havebeen used to vent these vapors external to the carburetor.

Early Quadrajet applications vented these vapors t othe atmosphere through an idle vent valve that is operated

mechanically . A wire tang on the pump lever opensthe valve during idle and allows the valve to close a tgreater throttle valve angles as in the off idle and par tthrottle positions .

Some models use a thermostatically controlled ven tvalve (Figure 8) . This heat sensitive valve is operated bya bi-metal strip which holds the valve closed at tempera-tures below 75°F . When temperatures at the carburetorexceed that value the valve opens allowing vapors toescape. The thermostatic vent valve is adjustable t omake sure it is timed to open during idle and closed a thigher engine speeds .

Figure 8 Thermostatic Idle Vent Valve

Figure 9 Bowl Vent Valve

Some Quadrajets have a vacuum operated vent valve(Figure 9) that is also controlled to function with a nevaporative vapor canister . The vacuum vent valve i sdesigned to be open and to allow fuel chamber vapor sto be routed directly to a vapor collection canister in-stead of the atmosphere for improved evaporativeemission control during engine shut-down . A passagebeneath the vacuum diaphragm in the air horn pro -

VACUUM PASSAGE

VACUUM VENT VALVE

VALV E

CONSTANT BLEEDRESTRICTIO N

VENT TOCANISTER

F'

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BOWL VENT VALVE TO CANISTER

FIXED IDLE AIR

BY-PAS S

DLE CHANNE LRESTRICTION

E MIXTURE

\HROTTLE

VALV ENEEDLE IDL EAIR/FUEL

HO

DISCHARGE HOLE

COMPENSATOR

LVE

IDLE

VA

T

FUEL

OFF-IDL EOPERATION

IDLE SYSTE M

Figure 10 Bowl Vent Valv e

vides a constant purge of the vapors from the vapo rcanister during off idle and higher engine speeds .

Later "modified" versions of the Quadrajet have abowl vent valve that is spring-loaded and is actuate dby action of a spacer on the pump plunger shaft (Figure10) . The fuel chamber is externally vented to the vapo rcollection canister during periods of engine shut-down.

Another method used to vent vapors is by the additio nof a tube to the air horn (see Figure 7) . Vapors flowthrough this tube and connecting hose to a vacuu moperated vapor vent valve that is an integral part of thevapor collection canister located elsewhere in the engin ecompartment . The canister vent valve is spring-loade dand normally open, allowing bowl vapors to pass into th ecanister during engine shut down. Manifold vacuumduring engine operation closes the valve and vapors ar epurged from the canister . This system improves hotengine starting and also meets government evaporativ eemission requirements .

NOTICE : External venting of fuel chambe rvapors is not 'used on Quadrajet carburetorsdesigned for marine use .

IDLE SYSTEMThe Quadrajet carburetor idle system is located o n

the primary side (fuel inlet side) of the carburetor t osupply the correct air/fuel mixture during idle and off-idle operation .

The idle system is used during this period becauseair flow through the carburetor venturi is not grea tenough to obtain efficient metering from the main dis-charge nozzles . The idle system is only used in the tw oprimary bores of the carburetor . Each bore has a separateand independent idle circuit (Figure 11) .

The idle system consists of a calibrated idle tube, ai rbleeds, idle channel restriction, idle mixture discharg ehole, and idle mixture screws or needles (one for eachbore) .

Figure 11 Idle System - Typica l

The idle system operates as follows :During curb idle (warm engine), the primary throttl e

valve is held slightly open by the idle speed screw orsolenoid plunger . The small amount of air passing be-tween the throttle valve and bore is regulated by ad-justing the position of the speed screw or solenoid plun-ger to obtain the desired idle speed . Since the enginerequires very little air for idle and low speed, fuel i sadded to the air to produce a combustible mixture b ythe direct application of vacuum (low pressure) fro mthe intake manifold to the idle discharge hole below th ethrottle valve . The idle discharge hole is in a very lowpressure area and the fuel in the fuel chamberis vented to atmosphere (high pressure through the ai rcleaner) . This causes fuel to flow from the fuel chamberdown through the main metering jet into the main fue lwell . It is picked up in the main well by the idle tubes(one for each bore) which extend into the fuel well . Thefuel is metered at the lower tip of the submerged idl etube and passes up through the tube . At this point, th efuel is mixed with air at the top of each idle tube throughthe top idle air bleed . The air bleed size is controlledby either a drilled hole or a brass insert dependin gupon carburetor application .

NOTICE: No attempt should be made toinstall a brass insert in those application sthat use a drilled hole for the top idle ai rbleed .

Then the fuel mixture crosses over to the idle dow nchannel where it is mixed with air at the side idle bleedlocated just above the idle channel restriction . The mix-ture continues down through the calibrated idle channe lrestriction past the lower idle air bleed and off-idl edischarge port where it is further mixed with air . Theair/fuel mixture moves down to the adjustable mixturescrew discharge hole where it enters the carburetor bor eand blends with the air passing by the slightly ope nthrottle valve . The combustible air/fuel mixture thenpasses through the intake manifold to the enginecylinders .

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The idle mixture screws are adjustable to blend thecorrect amount of air/fuel mixture from the idle syste mto the engine at idle . Turning the mixture screws inward(clockwise) decreases idle mixture discharge (gives aleaner mixture) and turning the mixture screws outward(counter-clockwise) increases idle mixture discharge(gives a richer mixture) .

OFF-IDLE OPERATIONAs the primary throttle valve is opened from cur b

idle to increase engine speed, additional fuel is neededto combine with the extra air entering the engine . Thi sis accomplished by the slotted off-idle discharge port .As the primary throttle valve opens, it passes by th eslotted off-idle discharge port, gradually exposing it tohigh manifold vacuum. The mixture added from the off-idle port mixes with the increasing air flow past theopening throttle valve to maintain the required air/fue lmixture of the engine .

Further opening of the throttle valve increases the ai rvelocity through the carburetor venturi sufficiently t ocause low pressure at the lower idle air bleed. As aresult, fuel begins to discharge from the lower idle ai rbleed hole and continues throughout operation of th epart throttle to wide-open ranges, thereby supplementin gmain discharge nozzle delivery .

The idle mixture screw discharge hole and off idl edischarge port continue to supply sufficient fuel fo rengine requirements until air velocity is high enoughin the venturi area to obtain efficient fuel flow from themain metering system .

The idle system functions in a similar manner in eachcarburetor bore.

The secondary throttle valves remain closed duringidle conditions and on some Quadrajet applications the yare coated with a special graphite material which isapplied at the factory to effectively seal the secondarythrottle valves in the bores for minimum air flow a tidle to prevent possible rough idle .

On many exhaust emission control carburetor applica-tions, the idle mixture screw discharge holes have bee nreduced in size . This was done to prevent a too richidle adjustment in the field should the idle mixture screw sbe turned out too far beyond normal idle mixture re-quirements . Also, starting in 1971, idle screw limite rcaps were added to emission control carburetors to dis-courage adjustment of the screws in the field . On latermodels, the idle mixture screws are sealed to preventreadjustment from the factory setting in the field .

ADJUSTABLE AIR BLEE DAnother feature added to some emission carburetors

is an adjustable off-idle air bleed system (Figure 11) . Aseparate air channel is added in the air horn which leads

Figure 12 Idle System - Late Model s

from the top of the air horn to the idle mixture crosschannel . An adjustment screw with a tapered head i smounted at the top of the channel and is used to con-trol the amount of air bleeding into the idle system .The off-idle air bleed is adjusted at the factory to main-tain very accurate off-idle air/fuel mixture ratios . It isadjusted during carburetor flow test and no attemptshould be made to readjust in the field . A triangularspring clamp forced over the vent tube covers the scre wto protect the adjustment from being tampered with an dit should not be removed . All service air horns have thisscrew preset at the factory .

FIXED IDLE AIR BY-PASSA fixed idle air by-pass system is used on some ap-

plications which consists of air channels that lea dfrom the top of each carburetor bore in the air hor nto a point below each throttle valve . At normal idle ,extra air passes through these channels supplementin gthe air passing by the slightly open throttle valves . Thepurpose of the idle air by-pass system is to reduce th eamount of air going past the throttle valves so that theyare nearly closed at idle . This reduces the amount ofair flowing through the carburetor venturi to preven tthe main discharge nozzles from feeding fuel durin gidle operation . The triple venturi system is very sensi-tive to air flow and where large amounts of idle airare needed to maintain idle speed, the fixed idle ai rby-pass system is used .

PURGE PORTIN GTo meet evaporative emission standards on late mode l

Quadrajet applications, fuel vapors from the carbu-retor float bowl and fuel tank are collected in a vapo rcanister and not vented to atmosphere . On many of these

CANISTER

THROTTLEPURGE TUBE

VALVE

IDLE

IDLE DISCHARG EMIXTURE

OFFIDLE

HOL E-

NEEDL E

E.G .R. (EXHAUST GAS

CANISTER PURG ERECIRCULATION)

IDLE SYSTEM

OFF-IDLEOPERATIO N

PORT CONSTANT

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carburetor models, vacuum ports are located in thethrottle body for canister purge . The purge ports leadthrough passages to a tube in the throttle body whic hconnects by a hose to the vapor canister .

The purge ports may consist of a constant (fixed )canister purge and a separate timed canister purge, ora timed canister purge only (Figure 12) .

The purge system operates as follows :

CONSTANT CANISTER PURG EThe constant canister purge port operates during idl e

operation of the engine . It is located below the throttlevalves to provide a constant purge of the canister when-ever the engine is running . As the throttle valves areopened beyond the idle position, additional purge of th ecanister is provided by each of the timed purge ports .

TIMED CANISTER PURG EThe timed canister purge ports operate during off-idle ,

part throttle, and wide-open throttle operation . They arelocated above the throttle valve in each bore next to th eoff-idle discharge port . The timed purge ports supplementthe constant canister purge port (where used) to provide alarger purge capacity for the vapor canister and to pre -vent over-rich mixtures from being added to the carbu-retor metering at any time.

On some applications (see Figure 12), the constantpurge port is used as the vacuum source to the EarlyFuel Evaporation (E.F.E.) Valve located in the exhaustmanifold . On these models, purging of the canister i saccomplished through the Positive Crankcase Ventilation(P.C.V.) system .

EXHAUST GAS RECIRCULATIO NAn Exhaust Gas Recirculation (E .G.R.) system, con-

sisting of an E.G.R. Valve, separate back-pressuretransducer valve (where used), vacuum hoses, an dvacuum supply ports in the Quadrajet carburetor, i sused on many vehicle applications to meet exhaustemission requirements . The E.G.R. valve is operate dby a vacuum signal taken from the carburetor . Thevacuum signal, dependent upon application, is takenfrom one or two punched ports located in the carbu-retor bore just above the throttle valves . Thus, E.G.R.valve operation is "timed" for metering exhaust gasesto the intake manifold dependent upon location of theports in the carburetor primary bore and by the degreeof throttle valve opening (See Figure 12) .

It is important that the E .G.R. vacuum signal port(s )not be exposed to manifold vacuum during engin eidle and deceleration to keep the E .G.R. valve closed.This prevents rough idle which can be caused by ex-cessive exhaust gas contamination in the air/fuel mix-tures .

TRANSMISSION CONVERTER CLUTC HSome applications have a port located above th e

throttle valve that is used to supply a timed vacuumsource for the automatic transmission converter clutch(see car division service manual for description of thi stransmission feature . )

HOT IDLE COMPENSATO RThe Hot Idle Compensator, when used on 4MV-4MC -

M4MC Quadrajet carburetors (See Figure 11), is locate din a chamber at the rear of the carburetor float bow ladjacent to the secondary bores . Its purpose is to offsetthe enriching effects caused by excessive fuel vapor sduring hot engine operation.

The compensator consists of a thermostatically-con-trolled valve, a heat sensitive bi-metal strip, and a valveholder and bracket . The compensator valve assembly isheld in place by a dust cover over the valve chamber .A seal is used between the compensator valve and th efloat bowl casting . The valve closes off an air channelleading from a hole in the top of the air horn, jus tbeneath the air cleaner, to a point below the secondar ythrottle valves .

Normally, the compensator valve is held closed bytension of the bi-metal strip. During extreme hot engineoperation, excessive fuel vapors entering the enginemanifold cause richer than normally required mixtures ,resulting in rough engine idle and stalling. At a pre-determined temperature, when extra air is needed tooffset the enriching effects of these fuel vapors, th ebi-metal strip bends and unseats the compensator valve .This uncovers the air channel leading from the valvechamber to the point below the throttle valves . Thisallows enough air to be drawn into the engine manifol dto offset the richer mixtures and maintain a smoot hengine idle . When the engine cools and the extra air i snot needed, the bi-metal strip relaxes, closes the valve ,and operation returns to normal mixtures .

For proper idle adjustment when the engine is hot ,the compensator valve must be closed . To check this, afinger may be held over the compensator air inletchannel located on top of the air horn. If no drop inengine RPM is noted on a tachometer, the valve isclosed. If the valve is open, plug the hole or cool enginedown to a point where the valve automatically closes fo rproper idle adjustment .

NOTICE : Plug the compensator hole with apencil or something that will be seen, asthe plug must be removed before the aircleaner is installed . Otherwise the compen-sator will not function if the plug is left i nthe hole .On some applications, the air inlet to the hotidle compensator is located beneath the airvalve in the secondary bores . The air inlet inthis location improves idle quality when the I

9D-5March 198 1Page 1 2

feeds additional fuel at closed choke for good cold enginestarting . Calibrated air bleeds, located in the air horn ,are used with this system .

The air-velocity sensitive pull-over enrichment systemallows the use of slightly leaner mixtures during par tthrottle operation and still provides enough fuel durin ghigh speed operation . This feature gives added refine-ment to the fuel mixtures for exhaust emission con-trol .

MAIN WELL AIR BLEED TUBE SSome 4MV Quadrajet applications use Main Wel l

Air Bleed Tubes in place of the main well air blee dholes (Figure 16) . The tubes, extending further into eachprimary bore, help main discharge nozzle response a sthe main metering system starts to feed fuel .

MAIN METERING SYSTEM M4MC-M4M EMODELS

Starting in the 1975 model year, major casting change swere made to the air horn, float bowl, and throttl ebody of the Quadrajet carburetor to incorporate a ne wAdjustable Part Throttle (A .P.T.) feature and, on som eapplications, the addition of an auxiliary power pistonand metering rod assembly. These new models weretermed "modified" and designated by the prefix "M"to the model listing (e .g ., M4MC) .

ADJUSTABLE PART THROTTLEThe A.P.T. feature on these "modified" models con-

sists of an adjustable metering rod assembly with fille rspool (Figure 17-A) or combination aneroid - meterin grod assembly (for an explanation of aneroid, see AltitudeCompensation, below) . The adjustable metering rod ,with or without aneroid, provides close tolerance controlof fuel flow to the main metering system during th epart throttle range .

The A.P.T. adjustment is performed at the factor yduring flow test by turning the threaded metering rod ,or aneroid-metering rod assembly, up or down to positionthe metering rod in a fixed metering jet located at thebottom of the fuel reservoir in the float bowl . This set sthe part throttle air/fuel mixture to the desired flow band .

ALTITUDE COMPENSATIO NOn M4MCA-M4MEA models, a barometric pressure -

sensitive aneroid, sometimes called a "bellows", is in-cluded as an integral part of the threaded A .P.T .metering rod assembly (Figure 17-B) . The aneroid, beingsensitive to air pressure change, automatically eitherexpands or contracts with changes of altitude to lowe ror raise the metering rod in the fixed metering jet tomaintain control of part throttle air/fuel ratios .

Figure 17 Adjustable Part Throttle - Modifie dModel s

Figure 18 Separated Main Well s

NOTICE : The position of the A .P.T. meter-ing rod in the fixed jet is extremely critical .Adjustment should NEVER be attemptedunless a replacement is required . The threadedA.P.T. metering rod should be adjuste dcarefully following adjustment procedures (Seestep 7a, page 38) .

As a result of these changes, a new float assembly ,plastic filler block (located in the top of the float cham-ber over the float valve), and new air horn gasket ar eused with the "modified" carburetor models .

SEPARATED MAIN WELLSThe main metering system of most later "modified "

Quadrajet models (Figure 18) operates similarly to tha tdescribed for 4MV-4MC models, above, except the floatbowl casting is revised to provide for separated mainwells . The separated main well feature is used to feedeach main nozzle for improved fuel flow through thecarburetor venturi . On these models, a special aneroidcavity insert is used in the fuel chamber to replace theadjustable metering rod assembly with filler spool, oraneroid-metering rod assembly, formerly used .

FIXED JET

MAIN METERIN GRODS (2)

MAIN METERING

FIXED JE TJETS (2 )

A .P .T . METERING ROD ASSEMBLIES [Modified Design )

MAIN WELL AI RBLEEDS

MAIN POWER PISTON

f

r' THROTTLE VALVES(DOWN)

MAI NPOWER PISTON

I

MAIN

METERING

SPRING

VACUUMMETERING

ROD SPASSAGE JET

S

MAIN METERING SYSTE M

FACTORY-METERINGADJUSTMENT SCREW

9D. 5March 198 1

Page 1 3

ADJUSTABLE PART THROTTLE FEATUR EOn "modified" Quadrajet carburetors that use sepa-

rated main wells, the A .P.T. adjustment consists of apin pressed in the side of the power piston which ex-tends through a slot in the side of the piston well . Whenthe power piston is down (economy position), the pinstops on top of a flat surface of the adjustment screwlocated in a cavity next to the power piston (See Figure18). The adjustment screw is held from turning by atension spring beneath the head of the screw .

During production flow test, the adjustment screw i sturned up or down which, in turn, places the taperedmetering rod at the exact point in the metering jet orificeto obtain the desired air/fuel mixture ratio to meetexhaust emission requirements .

NOTICE : The A.P.T. screw is preset at thefactory and no attempt should be made t ochange this adjustment in the field . If a floatbowl replacement is required during carbu-retor service, the new service float bowl as-sembly will be supplied with the adjustmentscrew preset as required .

POWER SYSTEMThe power system in the Quadrajet carburetor pro-

vides extra mixture enrichment to meet power require-ments under heavy engine loads and high-speed opera-tion. The richer mixtures are supplied through themain metering system in the primary and secondarysides of the carburetor (Figure 19) .

The fuel mixture is enriched in the two primary boresthrough the power system . This consists of a vacuu moperated power piston and a spring(s) located in a cyl-inder connected by a passage to intake manifold vacuum .The spring(s) under the power piston apply an upwar dforce against manifold vacuum force tending to pull thepiston downward .

During part throttle and cruising ranges, manifol dvacuum is sufficient to hold the power piston dow nagainst spring force so that the larger diameter of th eprimary metering rod tip is held in the main meteringjet orifice to provide leaner mixtures during these periodsof engine operation . However, as the engine load i sincreased to a point where extra mixture enrichment i srequired, the power piston spring force overcomes thevacuum pull on the power piston and the tapered ti pof the primary metering rod moves upward in the mai nmetering jet orifice . The smaller diameter of the meteringrod tip allows more fuel to pass through the main meter-ing jet and enrich the fuel mixture to meet the adde dpower requirements . As engine load decreases, the mani-fold vacuum rises and extra mixture enrichment is n olonger needed . The higher vacuum pulls downward o nthe power piston against spring force which moves thelarger diameter of the metering rod into the metering

Figure 19 Power Syste m

jet orifice returning the fuel mixture to normal econom yranges .

Dual power piston springs are used beneath the powerpiston in the piston bore of some 4MV-4MC Quadrajetmodels (Figure 19) . A smaller diameter power pistonspring seats in the center of the piston and bottom son the float bowl casting . The spring is used to controlpower enrichment during light engine loads . A largerdiameter spring surrounds the smaller inner spring an dexerts additional pressure on the bottom of the powe rpiston to provide efficient mixture ratios at heavier engineload conditions . The dual power piston spring feature ,on models so equipped, assists in providing improvedfuel control of air/fuel mixture ratios to meet emissionand power requirements of the engine .

POWER SYSTEM - MECHANICA LOPERATION

Some Quadrajets have a mechanical power enrichmentsystem in addition to the vacuum enrichment feature .This provides accurate control of fuel mixtures at highengine speeds and load and yet allows the use of vacuu menrichment for improved fuel control during mediu mengine loads .

The mechanical enrichment is controlled by a stempressed into the base of the power piston which extend sinto the throttle body. The stem is operated by a leve rwhich is hinged to the throttle body casting and a ca mon the center of the throttle shaft . When the throttlevalves are opened to a pre-determined point, the ca mon the throttle shaft forces the lever upward until i tcontacts the stem on the power piston and pushes th ecomplete piston assembly upward against engine vacuum(Figure 20) . This, in turn, lifts the metering rods ,placing the smaller diameter of the metering rods inthe main metering jets for positive mixture enrichmen tat greater throttle valve openings .

The power piston has a "trapped" spring which limitsthe travel of the piston during vacuum operation . Thespring is retained between the piston and a fluted

AIR VALVE S

(OPE N I

METERING MAIN -SECONDARYDISCS DISCHARGE THROTTLE VALVE SMAIN

NOZZLESMETERING

RODS

POWER PISTON

MAI NSPRING

METERIN GVACUUM JETSPASSAGE

POWER SYSTEM

9D-5

March 198 1

Page 14

Figure 21 Multiple Stage Power Syste m

POWERPISTON (UP )

MECHANICAL POWER SYSTEM

POWER SYSTE M

MAI NMAIN

POWE R

AUXILIARY

METERING PISTON (UP)

METERING ROD (I)

ROOS 121

SECONDARY METERING ROOS (2)

ACCELERATORWELL & TUB E

ACCELERATING WELL POR T

METERIN GROD LEVER

Figure 20 Mechanical Power Enrichmen t

washer on the power piston stem . The washer is re-tained with a "C" clip located in a groove on the powe rpiston stem .

During high engine vacuum, the power piston sprin gis compressed and the fluted washer and piston areseated at the bottom of the power piston cavity . Asengine load increases, vacuum drops and the powe rpiston moves upward against spring tension until th e"C" clip seats against the fluted washer . No more enrich-ment will take place until the pin in the power pistonis contacted by the mechanical enrichment lever . Asthe throttle valves are opened further, the complet epower piston assembly is forced upward placing thesmaller diameter of the metering rods in the jets fo rmaximum enrichment at higher engine speeds and loads.

When engine load and speed is decreased, the powerpiston will return to the down position, seating th efluted washer and piston in the bottom of the powerpiston cavity as high engine vacuum compresses th epower piston spring . This returns the metering syste mto leaner fuel mixtures for light engine loads .

MULTIPLE STAGE POWER ENRICHMENTIn some "modified" Quadrajet carburetors, a multipl e

stage power enrichment system, consisting of two powe rpistons (Figure 21), is used for more sensitive control ofair/fuel ratios during light duty engine power require-ments while providing for richer mixtures duringmoderate to heavy engine loads .

AUXILIARY POWER PISTO NAn auxiliary power piston and single metering rod

assembly, located in front of the main (primary) powerpiston, is used for light duty power requirements . Onlight throttle opening when manifold vacuum drops t oa predetermined point, the spring force under the auxiliar ypiston overcomes the vacuum pull and raises the piston

which lifts the single metering rod out of a fixed meteringjet . This provides partial fuel enrichment for light dutyengine loads .

MAIN (PRIMARY) POWER PISTONDuring moderate to heavy engine loads when a further

drop in manifold vacuum occurs with increased throttl eopening, the main (rear) piston spring force overcome sthe vacuum pull and raises the piston which lifts th etwo metering rods out of the metering jets for additionalfuel enrichment for heavy duty power requirements .

The multiple stage (two piston) power enrichmen tsystem is specifically calibrated for the power require-ments of each engine by controlling spring rates of eachpiston. The system requires no adjustment in the field ;however, the main (rear) power piston and meteringrod assemblies and the auxiliary (front) power pistonand metering rod assembly are removable for norma lcleaning and service replacement as needed .

NOTICE : The main (rear) and auxiliary(front) power piston springs must NOT b einterchanged . To prevent mixing of powerpiston springs at time of carburetor disas-sembly, lightly wrap a piece of masking tapearound the auxiliary power piston spring foridentification . Then, on reassembly, removethe tape and install the spring in the fron tlocation beneath the auxiliary power pisto nwith single metering rod .

POWER SYSTEM -TURBOCHARGER APPLICATION S

Some modified Quadrajet models are designed forTurbocharger applications . The power system in thes emodels operates in the same manner as previouslydescribed except for one important difference . Thevacuum supply, directed to the underside of the powe rpiston, is controlled externally by a Turbocharger Vacu-

9D- 5March 198 1

Page 1 5

Figure 22 Secondary System - Typica l

urn Bleed Valve . The vacuum signal is routed to thecarburetor through a hose from the bleed valve to a nexternal tube located on the side of the carburetor .

The power system operates as follows :

During part throttle and cruising ranges, engine loadis light and vacuum, from the Turbocharger Vacuu mBleed Valve, is sufficient to hold the power piston dow nagainst spring force and the larger diameter of th emetering rod tip is held in the metering jet for leanermixtures .

As engine load is increased to a point where extrafuel enrichment is required and the intake manifold i spressurized by the exhaust gas driven Turbocharger ,the vacuum bleed valve "switches" and reduces vacuumto the power piston to zero . At this point, spring forc eoperating on the power piston lifts the main meteringrods for increased fuel delivery .

The remote power enrichment feature, through thevacuum bleed valve, provides richer mixtures duringheavy engine loads and wide-open throttle power re-quirements when the intake manifold is pressurized bythe Turbocharger at a time when manifold vacuum i shigh enough tending to operate the power piston in th enormally "lean" position . In this way, the power syste mcontrols fuel metering during light and heavy powerrequirements .

SECONDARY SYSTEMThe primary stage of the Quadrajet carburetor pro-

vides adequate air and fuel for low speed operation .However, at higher speed, more air and fuel are needed

to meet engine demands . The secondary stage of thecarburetor provides the additional air and fuel throug hthe secondary throttle bores for power and performanc erequirements .

The secondary stage has a separate and indepen-dent metering system (Figure 22) . It consists of twolarge throttle valves connected by a shaft and linkageto the primary throttle shaft . Fuel metering is controlledby a spring-loaded air valve, secondary metering orificeplates, secondary metering rods, fuel wells with blee dtubes, fuel discharge nozzles, accelerating wells andtubes . These are used to modify fuel flow characteristicsfor exact air/fuel calibration .

The secondary metering system supplements fuelflow from the primary stage and operates as follows :

When the engine reaches a point where the primarybores cannot meet engine air and fuel demands, a leve ron the primary throttle shaft, through a connectinglink to the pick-up lever on the secondary throttle shaft ,begins to open the secondary throttle valves . This occursonly if the choke has warmed the thermostatic coi lsufficiently to release the secondary throttle valve lock -out lever (if used) .

As the secondary throttle valves open, engine mani-fold vacuum (low pressure) is applied directly beneaththe air valves . Atmospheric pressure on the top of th eair valves forces the air valves open against spring an dair valve dashpot forces, provided the choke coil haswarmed sufficiently to release the air valve lockout lever,if used . This allows air to pass through the secondarybores of the carburetor .

On most models, accelerating wells are used to supplyfuel immediately to the secondary bores . This preventsa momentary leanness until fuel begins to feed from th esecondary discharge nozzles. When the air valves begi nto open, the upper edge of each valve passes the ac-celerating well ports (one for each bore) . As the edge sof the air valves pass the ports, they are exposed tomanifold vacuum and immediately feed fuel from th eaccelerating wells located on each side of the fuel cham-ber. Each accelerating well has a calibrated orificewhich meters the fuel supplied to the well from th efuel chamber . Some models have the accelerating wel lports located beneath the front edge of the air valveinstead of above. These begin to feed fuel to the secon-dary bores almost instantly after the secondary throttl evalves open and before the air valves begin to open .This type of porting is used on some models wher eadded enrichment is needed during cold operationwhen the air valve is locked closed, and also provide san earlier cut-in of fuel from the ports than the model swhich have the port located above the valves . The useof either type of porting is dependent upon engine fueldemands .

The secondary main discharge nozzles (one for eachbore) are located just below the center of the air valve s

SECONDAR YACCELERATO R

WELLS & TUBE S

SECONDARY METERIN GORIFICE PLATES SECONDAR Y

DISCHARG ENOZZLE S

SECONDARY SYSTEM (Typical)

9D-5

March 198 1

Page 1 6

and above the secondary throttle valves . The nozzles ,being located in a low pressure area, feed fuel as follows :

As the secondary throttle valves are opened, atmos-pheric pressure opens the air valves . This rotates aplastic eccentric cam attached to the center of the airvalve shaft . As the cam rotates, it lifts the secondarymetering rods out of the secondary orifice plates throug hthe metering rod hanger which follows rotation of th eeccentric cam .

Fuel flows from the fuel chamber through the secon-dary metering orifice plates into the secondary mainwells where it is mixed with air from the secondarymain well air bleed tubes . The air emulsified fuelmixture travels from the main wells through the secon-dary discharge nozzles where it sprays into the secondar ybores . Here the fuel is mixed with air traveling throughthe secondary bores to supplement the air/fuel mixturedelivered from the primary bores and goes on into th eengine as a combustible mixture .

As the secondary throttle valves are opened furthe rand engine speeds increase, air flow through the secon-dary side increases and opens the air valves to a greate rdegree which, in turn, lifts the secondary meteringrods further out of the orifice plates . The metering rod sare tapered so that the fuel flow through the secondarymetering orifice plates is directly proportional to ai rflow through the secondary carburetor bores . In thi smanner, correct air/fuel mixtures through the secondar ybores are controlled by the depth of the metering rod sin the orifice plates .

The depth of the metering rods in the orifice plate sin relation to the air valve position are factory adjuste dto meet air/fuel requirements for each specific engin emodel — no change in this adjustment should be mad ein the field . Also, many models include a tang on th eair valve lever which contacts a stop on the air hor ncasting to control carburetor air flow capacity.

METERING RODS - PRIMARYThere are two types of primary main metering rods

used in the Quadrajet carburetors . 1968 and latermodels use a rod which has a double or multiple taperat the metering tip . The 1967 and earlier models have asingle taper at the metering tip .

Both rod types use a similar two-digit numberingsystem . The number indicates the diameter of themetering rod and is the last two digits of the part num-ber. The 1968 and later models will have a letter stampe don the rod after the two-digit number.

METERING RODS - SECONDAR YThe secondary rods are coded with a two-letter sys-

tem which corresponds directly to the part number .

(See Delco Bulletin 9A-100 for a complete descrip-tion and listing of metering rods) .

There are other features incorporated in the secondarymetering system as follows :

1. The secondary main well air bleed tubes exten ddownward into the main fuel well below normal fue llevel . These bleed air into the fuel in the secondar ywells to quickly emulsify the fuel with air for goodatomization and improved fuel flow from the secondarynozzles .

2. The secondary metering rods may have a milledslot at the larger diameter of the metering tip . Thepurpose of the slots is to ensure an adequate supply offuel in the secondary main wells when the air valves ar ein the closed position . At this point, the metering rodsare nearly seated against the metering orifice plates .The slot in the rod is adjacent to the orifice plate an dallows a small amount of fuel to pass between the meter -ing rod and metering disc . During extreme hot engineidle or hot soak, the fuel could boil out of the secondar yfuel wells . The milled slot allows enough fuel to by-pass the orifice plate and keep the main fuel wells ful lof fuel . This ensures adequate fuel supply in the mainwells at all times to give immediate fuel delivery fro mthe secondary discharge nozzles .

3. Some applications use secondary discharge nozzlesthat incorporate a vertically drilled cross hole locatedabout half way down the length of the nozzle . Thehole serves as an additional air bleed to assist air/fue lmixture distribution passing through the secondarydischarge nozzle .

4. A baffle plate, extending into each secondary bore ,is located just below the air valves on all models . Thebaffle extends up and around the secondary discharg enozzles to provide equal fuel distribution, as near a spossible, to all engine cylinders at lower air flows .

5. On some models, an integral baffle is added t othe bottom side of the secondary air valve. The baffleimproves mixture distribution from the secondary sideat higher air flows .

6. An air horn baffle is used on some models toprevent incoming air from the air cleaner reacting onthe secondary main well bleed tubes . The baffle is lo-cated adjacent to the secondary well bleed tubes an dextends above the air horn between the primary an dsecondary bores . This prevents incoming air from forcingthe fuel level down in the secondary wells through th ebleed tubes and prevents secondary nozzle lag on heav yacceleration .

7. Some models use notched secondary air valves toreduce the vacuum signal at the nozzles for leaner air/fuel mixture ratios during initial air valve opening . Theleaner mixtures assist in meeting emission requirement sand also improve throttle response when operating athigh altitudes .

AIR VALVE DASHPOTThe secondary air valves use an air valve dashpot

Delco

9D.5March 1981

Page 1 7

Figure 23 Air Valve Dashpot Design s

feature to control opening rate of the air valve . Thisprevents an uncontrolled air valve opening rate whic hresults in an instantaneous air rate change and a "lag-ging" fuel rate change as the secondary throttlevalves are opened . The dashpot, through linkage, con-trols opening of the air valves to provide a smoot htransition to secondary system operation .

There are two different types of air valve dashpotsused in the Quadrajet carburetor :

The early type dashpot (Top of picture, Figure 23 )consists of a piston which operates in a fuel well adjacen tto the float bowl . The piston stem is connected to th eair valve through a link and lever assembly . As the airvalves open, the dashpot piston is pulled upward forcin gfuel to flow between the side of the piston and fue lwell which retards the air valve opening . A rubbe rwasher attached to the piston stem acts as a check valve .During upward movement of the piston, the rubbe rwasher seats and forces all fuel to flow around the piston .When the air valve closes, the check valve unseats an dallows fuel to also pass through the center of the pis -ton allowing the air valves to return closed rapidly .

The late type air valve dashpot (Lower picture, Figure23) operates off of the front choke vacuum break dia-phragm unit . The secondary air valve is connected t othe choke vacuum break unit by a rod, to control theopening rate of the air valve. Whenever manifold vacuumis sufficiently high, the vacuum diaphragm is seated ,plunger retracted, against spring load . At this point ,the vacuum diaphragm link is in the forward end of theslot in the air valve lever, or in the rear of the slot inthe vacuum diaphragm plunger, and the air valves areclosed .

Figure 24 Pump Syste m

During acceleration or heavy engine loads when thesecondary throttle valves are opened, the manifoldvacuum drops . The spring located in the vacuum dia-phragm unit overcomes the vacuum force and move sthe plunger stem outward . This action allows the airvalves to open. The opening rate of the air valves i scontrolled by the calibrated restriction in the vacuuminlet of the diaphragm cover and the valve closing spring .The dashpot action, due to this restricted vacuum flowand spring force, provides the required delay in ai rvalve opening needed until sufficient fuel flows fromthe secondary discharge nozzles .

ACCELERATING PUMP SYSTEMDuring quick accelerations when the throttle i s

opened rapidly, air flow through the carburetor bore sand intake manifold vacuum change almost instanta-neously . However, the fuel which is heavier, tends tolag behind causing a momentary leanness . To preven tthis, the accelerator pump system is used to provid ethe extra fuel necessary for a smooth transition in engineoperation during this period .

The accelerating pump system is located in the primar ystage of the carburetor . It consists of a spring-loade dpump plunger and pump return spring (operating in afuel well), fuel passage, discharge check ball, retainer ,and pump jets, one in each bore (Figure 24) .

On most late Quadrajet models, an expander (garter)spring is used in the pump cup for constant pump cu pto pump wall contact . The pump cup is of the floatingdesign; i .e ., the up and down movement of the cup o nthe plunger head either "seats" to provide a solid chargeof fuel on the down-stroke, or "unseats" on the fillingof the pump well (up-stroke) . The cup remains unseatedwhen there is no pump plunger movement which allowsvapor to vent from the pump well .

AIR VALVE DASH POT OPERATION (EARLY )AIR VALVE SHAFT LEVE R

CLOSE D

OPEN±'ACTUATING RO D

VACUUM BREAKDIAPHRAGM ASSEMBLY

AIR VALVE DASHPO OPERATION (LATE )

AIR VALVE CLOSING SPRIN G

n LEVE R

r

/LIN K

PISTON ~~.

'HINGESTEM rlu ~~.

PIN

PUM PLEVER

DISCHARG Eyy PASSAG E

DISCHARG EBALL RETAINER

PUMP DISCHARGERETURN CHECK BALL

PUMP

SPRIN G

PLUNGER

EXPANDE RSPRIN G

PUMP SYSTEM

9D•5

March 198 1

Page 18

Delco

CHOKE ENRICHMENTFUEL CHANNE L

CHOKE VALVE

_ CHOKE ROD

/-`

I r-)FAST IDLE CA M

VACUUM BREA KLEVER AND TANG

VACUUM BREAKASSEMBL Y

'-~--UNIOADER TANGS

FAST IDLE SCREW

P

4M-2 5

Figure 25 Pump Stem Seal & Retainer

The pump plunger is operated by a pump lever onthe air horn which is connected directly to the throttl elever by a rod .

When the pump plunger moves upward in the pumpwell as happens during throttle closing, fuel from th efuel chamber enters the pump well through a verticalslot located near the top of the pump well . It flowspast the " unseated " pump cup to fill the bottom ofthe pump well and pump discharge passage .

When the primary throttle valves are opened, thepump rod and lever forces the pump plunger downward .The pump cup seats instantly and fuel is forced throughthe pump discharge passage where it unseats the pumpdischarge check ball and passes on through the passag eto the pump jets where it sprays into the venturi areaof each primary bore .

It should be noted the pump plunger is spring loaded .The upper duration spring is balanced with the bottompump return spring so that a smooth, sustained chargeof fuel is delivered during acceleration. Selection of theduration spring by the factory is used to control th edifferences in rate of movement between the pumplinkage and the plunger head for correct pump fue ldelivery .

The pump discharge check ball seats in the pumpdischarge passage during upward motion of the pumpplunger so that air will not be drawn into the passag eand prevent proper pump fill .

During higher air flows through the primary bores ,a vacuum exists at the pump jets . A passage, locate djust behind the pump jets, leads to the top of the ai rhorn to vent the pump fuel circuit outside the carburetorbores . This acts as a suction breaker so that when thepump is not in operation, fuel will not be pulled out ofthe pump jets into the venturi area . This insures a fullpump stream when needed and prevents any fuel "pull -over" from the pump discharge passage .

Figure 26 Choke System-4M V

In order to keep evaporative emission levels to aminimum, later model M4ME-M4MC models have apump plunger stem seal and retainer located in the ai rhorn . In the event of service repair or cleaning of th ecarburetor, a new seal and retainer should be installed(See Figure 25) .

CHOKE SYSTE MThe Quadrajet choke valve is mounted in the air

horn located above the carburetor primary venturi . Aclosed choke valve provides the correct air/fuel mixtur eenrichment to the engine for good cold engine startin gand when partially open smooth running during th ewarm-up period . The secondary throttle valves, or airvalve on some models, are locked closed until the engineis thoroughly warm and the choke valve is wide open .

The Model 4MV choke system (Figure 26) consists ofa choke valve, vacuum break diaphragm assembly ,thermostatic coil-mounted on the intake or exhaustmanifold, fast idle cam, and connecting linkage .

Heat from exhaust gases is used for control of thermo-static coil temperature . Choke operation is controlle dby a combination of intake manifold vacuum, the off -set choke valve, temperature, and throttle position .

The thermostatic coil is calibrated to hold the chokevalve closed when the engine is cold .

The choke system operates as follows :

When the engine is cold, prior to starting, depressin gthe accelerator pedal to the floor opens the carburetorthrottle valves. This allows the fast idle cam followerlever to clear the steps on the fast idle cam . At thispoint, torque from the thermostatic coil closes the chokevalve and rotates the fast idle cam so that the cam fol-lower lever comes to rest on the highest step of th efast idle cam . (This opening of the throttle valves also

Delco

9D . 5March 198 1

Page 1 9

pumps a priming mist of fuel through the pump jetsinto the primary throttle bores to aid starting) . Duringcranking, engine vacuum below the choke valve pull sfuel from the idle system and main discharge nozzles .This provides adequate enrichment for good cold starts .

Some Quadrajet models use a choke enrichment fue lsystem to supplement fuel feed from the primary mai ndischarge nozzles for good cold engine starting .

Two calibrated holes, one in each primary bore, ar elocated in the air horn just BELOW the choke valv eto supply added fuel for cold enrichment during thecranking period. The extra fuel is supplied throug hchannels which lead to the secondary accelerating wel lpickup tubes to allow fuel at closed choke to be draw nfrom the secondary accelerating wells located in the floatbowl chamber, (As shown in Figure 26) . Also, duringwarm engine operation, the two calibrated holes in th eair horn feed a small metered amount of fuel at higherair flows to supplement fuel flow in the primary boresto provide the extra fuel needed at higher engine speeds .

As mentioned earlier (See Main Metering System) ,other Quadrajet models use the fuel pull-over enrich-ment system. This system is similar to the chokeenrichment fuel system except that two calibrated holes ,one in each primary bore, are located in the air hornjust ABOVE the choke valve to supply added fuel duringhigher carburetor air flows. The calibrated holes, locatedabove the choke valve, do not feed fuel at closed chokeduring the engine cranking period .

When the engine starts and is running, manifol dvacuum is applied to the vacuum break diaphragmunit mounted on the side of the float bowl . This move sthe diaphragm plunger in until it strikes the rear cover ,thereby opening the choke valve to a point where theengine will run without loading or stalling . (This is calledthe "vacuum break" position) . At the same time, thefast idle cam follower lever on the end of the primarythrottle shaft will drop from the highest step on th efast idle cam to a lower step when the throttle is opened .This gives the engine sufficient fast idle and correctfuel mixture for running until the engine begins t owarm up and heat the thermostatic coil .

As the engine continues to warm up, heat graduallyrelaxes tension of the thermostatic coil to allow thechoke valve to continue opening through air pressur epushing on the offset choke valve and the weight of th elinkage pulling the choke valve fully open at which pointthe engine can run at normal air/fuel mixtures .

The fast idle cam has graduated steps so that the fas tidle speed is lowered gradually during the engine warm-up period . The fast idle cam movement (and ste pposition) is a function of choke valve position . Whenthe engine is warm and the choke valve is completel yopen, the fast idle cam follower will be off the stepsof the fast idle cam. At this point, the idle speed screwor solenoid controls normal (warm) engine idle speeds .

Figure 27 Secondary Throttle Valve Lockou t

SECONDARY THROTTL EVALVE LOCKOUT

A secondary throttle valve lockout feature is used onmany Quadrajet models to prevent opening of the secon-dary throttle valves during cold operation when wide -open accelerations could cause possible engine damag eor excessive wear (Figure 27) . On these applications ,a lockout lever, located on the float bowl, is weightedso that a tang on the lower end of the lever catches alock pin on the secondary throttle shaft and keeps th esecondary throttle valves closed. As the engine warmsup, the choke valve opens and the fast idle cam drops .When the engine is thoroughly warm, the choke valv eis wide open and the choke coil pulls the intermediatechoke lever completely down and the fast idle ca mdrops down so that the cam follower is completely of fthe steps of the cam. As the cam drops the last fewdegrees, it strikes the secondary lockout lever and pushe sit away from the secondary valve lockout pin . Thisallows the secondary throttle valves to open and operat eas described under the Power System .

AIR VALVE LOCKOU TSome Quadrajet carburetors incorporate an air valve

lockout feature (Figure 28), instead of the secondar ythrottle valve lockout, whereby the air valves are locke dclosed until the engine is thoroughly warm and thechoke valve is wide open . An air valve lockout lever ,mounted on the air horn, is so weighted that a tang o nthe lever catches the upper edge of the air valve andkeeps the air valves closed when the choke valve is closed.When the thermostatic coil warms up it moves the chok evalve toward the open position, the end of the chokerod moves upward and strikes a tang on the air valvelockout lever . As the choke rod moves up to the end o fits travel, it pushes the lockout tang upward and un-locks the air valve .

CHOKE SYSTEM (WITH SECONDARYLOCKOUT FEATURE)

4M-2 6

SECONDAR Y LOCKOUT LEVER

FAST IDLE CAMFOLLOWER

9D• 5

March 198 1

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Delco

Figure 28 Air Valve Lockou tAlso, some early model 4MV carburetors use a vacuu m

break modulating spring and split choke spring (Figur e28) . The vacuum break modulating spring allows th evacuum break (choke valve position) to vary accordin gto ambient temperature. The vacuum break modulatingspring, connected to the vacuum break link, allow svarying choke openings depending on the closing forceof the thermostatic coil . As the closing force of the coilincreases (cool weather), the link is allowed to move i nthe slotted lever until the modulating spring overcomesthe coil force, or the link is in the end of the slot . Thisresults in less vacuum break during cooler weatherand more vacuum break during warmer weather .

The split choke feature operates during the last fewdegrees of choke thermostat rotation. The purpose is tomaintain the fast idle speed long enough to keep th eengine from stalling, but allow the use of a choke coi lwhich lets the choke valve open quickly. The operatio nof the split choke feature is controlled by a torsion springon the intermediate choke lever shaft . As explaine dearlier, air pressure action on the offset choke valv etends to force the choke valve open against tension o fthe choke thermostatic coil . In the last few degreesof thermostatic coil opening motion, a tang on the inter -mediate choke lever contacts the end of the torsio nspring . This keeps the fast idle cam follower lever o nthe last step of the fast idle cam longer to maintainfast idle until the engine is thoroughly warm. The springworks against the thermostatic coil until the coil is hotenough to pull on the intermediate choke lever and over -come the torsion spring tension . The torsion springmust be placed in the specified notch in the vacuumbreak mounting bracket for application used .

On all 4MV models, the choke system is equippe dwith an unloader mechanism which is designed to par-tially open the choke valve, should the engine becomeloaded or flooded . To unload the engine, the acceleratorpedal must be depressed so that the throttle valves ar eheld wide open. A tang on a lever on the choke side of

Figure 29 Spring Assist Choke Closing Syste mthe primary throttle shaft contacts the fast idle ca mand through the intermediate choke shaft forces thechoke valve slightly open . This allows extra air to ente rthe carburetor bores and pass on into the engine mani-fold and cylinders to lean out the fuel mixture so tha tthe engine will start .

CHOKE SYSTEM WITH SPRING ASSIS TCHOKE CLOSING SYSTE M

Some 4MV carburetors use a spring assist chok eclosing system (Figure 29) . The assist spring is of thetorsion type and is added to the intermediate chokeshaft . It exerts pressure on the vacuum break lever t oforce the choke valve toward the closed choke position .The tension of the torsion spring is overcome by th echoke thermostatic coil located on the engine manifol dwhich, during the engine warm up period, will pull thechoke valve open . The addition of a torsion springassists in closing the choke valve to ensure good enginestarting when the engine is cold .

Along with the choke closing assist spring, certain4MV models use the fast idle cam "pull-off" feature .

When the engine starts and is running, manifoldvacuum is applied to the vacuum break diaphragm an dthe diaphragm plunger moves slowly inward to ope nthe choke valve . As this happens, a tang on the plunge rcontacts the end or "tail" of the fast idle cam to "pull -off" the cam from the high step to the lower secon dstep setting .

A slight change in the method of vacuum break ad-justment is required on these models that use the fas tidle cam "pull-off ' feature . (See Adjustment Proceduresin the 9D-5 Section of the Delco Carburetor Parts an dService Manual 9X) .

CHOKE SYSTEM WITH VACUUM BREA KCLOSING ASSIST SPRIN G

Other 4MV models have the choke closing assis t

CHOKE SYSTEM

4M-27

% ~ VACU U+^~ BREAK

THERMOSTATIC

/ /

ASSEM Y

COIL AND ROD

w!j- `~

11 UNLOADERTANGS

FAST IDLE SCREW

AIR VALVESHAFT LEVER

VACUUM BREAK7ADJUSTMENT TANG

VACUUM BREA KASSEMBL Y

SECONDAR Y LOCKOUT LEVER

FAST IDLE CAMFOIIOWER

4M-28

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9D-5March 1981

Page 2 1

Figure 30 Vacuum Break Closing Assist Sprin g

spring located on the vacuum break plunger stem re -placing the torsion spring located on the intermediatechoke shaft (Figure 30) .

The choke closing assist spring aids in closing th echoke valve along with tension from the remote chokethermostatic coil for improved engine starting. Thechoke closing assist spring only exerts pressure on th evacuum break link to assist in closing the choke valveduring engine starting. When the engine starts and thechoke vacuum break diaphragm seats, the closing springretainer hits a stop on the plunger stem and the assis tspring no longer exerts pressure on the choke valve .

The vacuum break diaphragm plunger is slotted toallow for free travel of the air valve dashpot link . Theslot is moved from the air valve shaft lever to the vacuumbreak plunger . A change in air valve dashpot adjust-ment procedure is required. (See Adjustment Proceduresin the 9D-5 Section, Delco Carburetor Parts and ServiceManual 9X) .

CHOKE SYSTEM WITH DELAYE DVACUUM BREAK FEATUR E

To delay the choke valve from opening too fast, some4MV models use a delayed vacuum break system . Aninternal delay valve is included inside the diaphragmunit (Figure 31) .

The delay feature operates as follows :

When the engine starts, vacuum acting on the interna ldelay valve bleeds air through a small hole in the valv ewhich allows the vacuum diaphragm plunger to mov eslowly inward . This gives sufficient time to overcomeengine friction and wet the engine manifold to preven ta lean stall . When the vacuum break diaphragm is full yseated, which takes a few seconds, the choke valv ewill remain in the vacuum break position until theengine begins to warm and relax the thermostatic coi llocated on the exhaust crossover in the intake manifold .

In addition to the internal delay valve, some car

Figure 31 Delayed Vacuum Break Feature

Figure 32 Vacuum Break Bucking Sprin gapplications have a separate vacuum delay tank addedto the system . This is connected "in series " to a secon dvacuum tube on the vacuum diaphragm unit to furtherdelay the choke vacuum break diaphragm operation .

The delay valve in the choke vacuum diaphragm uni tis designed to "pop " off its seat and allow the diaphrag mplunger to extend outward, when the spring force agains tthe diaphragm is greater than the vacuum pull . Thiswill give added enrichment as needed on heavy accelera-tion during cold drive-a-way by allowing the choke coilto slightly close the choke valve . Some 4MV modelsuse a calibrated restriction in the vacuum inlet to th evacuum break diaphragm unit in place of the interna ldelay valve . Similar to the internal delay valve, the cali-brated restriction delays the supply of vacuum to th ediaphragm unit to retard opening of the choke valve forgood engine starting .

CHOKE SYSTEM WITH VACUU MBUCKING SPRIN G

A spring-loaded plunger is used in the vacuum brea kunit on some 4MV models (Figure 32). The purpose ofthe spring, called a "bucking spring", is to offset chok ethermostatic coil tension and balance the opening o fthe choke valve with tension of the choke coil . This

AIR VALVESHAFT LEVER

CHOK EROD

CHOKE CLOSINGASSIST SPRIN G

FAST IDLE CA M

THERMOSTATI CCOIL AND RO D

CHOKE SYSTEM

`00,,V1

oar 7

ASSEMBL Y

NrLOADER TAN G

FAST IDLE SCRE W

AIR VALVEAIR VALV EDASH-POT ROD

VACUUM BREA K

SECONDAR YLOCKOUT LEVE R

FAST IDLE CAMFOLLOWER

.4;..CHOKE COI LLEVER

CHOKE VALVE r

.0416-Ili

VACUUM BREAK LEVER

1

FAST IDLE -

O UNIT

~t4S aCHOKE ROD

CHECK BLEE DVALVE

PLASTI CRETAINER AIR BLEED

CHOKE SYSTE M

FILTE RSCREEN

VACUUM BREAK BUCKING SPRING

9D-5

March 1981

Page 22F'

Delco

enables further refinement of air/fuel mixtures becausethe coil, which senses engine and ambient temperatures ,will allow the choke valve to open gradually againstspring tension in the diaphragm plunger head. In otherwords, in very cold temperatures, the extra tensioncreated by the thermostatic coil will overcome the ten-sion of the diaphragm plunger (bucking) spring toprovide less choke valve opening with the result o fslightly richer mixtures . In warmer temperatures, thethermostatic coil will have less tension and, consequently ,will not compress 'the spring as much thereby giving agreater choke valve opening for slightly leaner mixtures .

CHOKE SYSTEM WITH DUAL DELAYE DVACUUM BREAK SYSTE M

Other Quadrajet carburetors use a dual delayedvacuum break system consisting of front and rear vacuu mbreak diaphragm units (Figure 33) .

The dual delayed vacuum break system operates asfollows :

During engine cranking, the choke valve is held close dby the tension of the thermostatic coil . This restricts ai rflow through the carburetor to provide a richer startingmixture .

When the engine starts and is running, manifold vacu-um is applied to both vacuum break units which ar emounted on the side of the float bowl . The front (pri-mary) vacuum break diaphragm opens the choke valveto a point where the engine will run without loading orstalling. As the engine is wetted and friction decreasesafter start, a delay valve in the rear (auxiliary) vacuu mbreak unit causes a delayed action to gradually ope nthe choke valve a little further until the engine wil lrun at a slightly leaner mixture to prevent loading .

A plunger "bucking spring" may be included on th ediaphragm plunger of the rear diaphragm unit (Seeexplanation, plunger bucking spring operation) .

A clean air purge feature is added to the rea rvacuum break diaphragm unit on some 4MV model susing the dual delayed vacuum break system (Figure 33) .A clean air bleed, added to the tube at the rear of therear vacuum break unit and located beneath a rubbe rcovered filter, purges the system of any fuel vapor sand dirt which possibly may enter the internal dela yvalve to disrupt operation . A change in adjustmentprocedure for setting the rear vacuum break is require don those models using the clean air purge feature . (SeeAdjustment Procedures, Section 5, of the Delco Car-buretor Parts and Service Manual 9X) .

CHOKE SYSTEM - 4MC (EARLY)The model 4MC carburetor differs from the 4MV

model in that the thermostatic choke coil is located i na choke housing, mounted directly to the side of thecarburetor float bowl, instead of a "remote choke "coil mounted on the intake or exhaust manifold .

Figure 33 Dual Delayed Vacuum Break Syste m

Figure 34 Early 4MC Choke Syste m

On 4MC models, engine vacuum is supplied throug han orifice in the choke housing which pulls heat fro mthe manifold heat stove into the choke housing andheat gradually relaxes choke coil tension . This allowsthe choke valve to continue opening through inlet ai rpressure pushing on the offset choke valve and theweight of the choke linkage pulling the valve open .

On early model 4MC carburetors (Figure 34), th evacuum break diaphragm is mounted integrally with th echoke housing located on the float bowl . An adjustabl eplastic plunger is included as a part of the vacuumbreak diaphragm . During cold operation after th eengine starts and is running, manifold vacuum applie dto the vacuum diaphragm pulls the diaphragm inwar dand the plunger strikes the vacuum break tang insidethe choke housing which, in turn, rotates the inter -mediate choke shaft and through connecting linkageopens the choke valve to the "vacuum break" position .

CHOKE SYSTEM - 4MC (LATE)The choke housing on later model 4MC carburetor s

DUAL DELAYED VACUUM BREA K

PLUNGER BUCKIN GSPRIN G

THERMOSTATI CCHOKE COI L

CHOK EROD

I

THERMOSTATI C

VACUUM

COIL

- -IIIVACUUM BREA K

ADJUSTING SCRE W

VACUUM BREA KTAN G

CHOKE SHAFTAND LEVER f' CHOK E

VALV E

EARLY 4MC CHOKE SYSTEM

9D-5

March 1981

Page 23

Figure 35 Later 4MC Choke Syste m

(Figure 35) is also located on the float bowl, but with aseparately mounted vacuum break diaphragm unit .The vacuum diaphragm unit on some 4MC models in-cludes an internal delay valve for good control of chokemixtures during the engine warm-up period (see descrip-tion of Delayed Vacuum Break System, Figure 31) .

CHOKE SYSTEM - M4MC-M4MCASimilar to 4MC models, an integral choke housin g

and an exhaust heated air thermostatic coil assembl yare mounted on the carburetor float bowl on M4MC-M4MCA models (Figure 36). A single or a dual vacuumbreak system is used for control of choke mixtures duringthe warm-up period . A special adjusting screw is in-cluded on the front vacuum break unit on all "modified"Quadrajet models. The vacuum break is adjusted byturning this screw to position a tang on the plungerthat contacts the vacuum break lever .

On some models, the front and/or rear vacuum brea kunits are delayed in operation by an internal delay valve(see inset, Figure 36) . The valve delays opening of thechoke valve a few seconds to allow the engine to ru non richer mixtures .

A clean air purge feature is used in either the fron tand rear vacuum break diaphragm units or in the rearunit only, depending upon carburetor application, toprevent dirt from plugging the internal delay valve . Afilter element is installed internally with a small blee dhole located in the end cover of the diaphragm unit .During engine operation, vacuum acting upon the dia-phragm pulls a small amount of filtered air through th ebleed hole in the end cover to purge the system of anyfuel vapors or dirt contamination which might be pulle dinto the internal delay valve located inside the diaphragmunit . During adjustment of the front and rear vacuu mbreaks, it will be necessary to plug the end cover ofthe vacuum break unit with tape, making sure to sea lthe small bleed hole .

Figure 36 M4MC-M4MCA Choke System (Typical )

Also, a vacuum inlet check ball may be used in th evacuum inlet tube on the front and rear vacuum brea kunits . The purpose of the inlet check ball is to preven texcess dirt and vapor contaminants from plugging th esmall internal delay valve in the diaphragm unit i ncase of engine "backfire " or "dieseling" conditions .

The rear vacuum break unit on some applicationsmay include a tension (bucking) spring in the diaphragmplunger head . (See previous explanation Plunger BuckingSpring Operation Page 21) .

On some M4MC-M4MCA models, the rear vacuu mbreak unit includes _a choke closing assist spring (SeeFigure 30 and previous explanation of closing assis tspring operation Page 20) .

Some M4MC-M4MCA models incorporate the "trap-ped stat" thermostatic coil design whereby the en dof the thermostatic coil is installed in a slot in the coi lpick-up lever inside the choke housing . In this way ,the coil is kept in contact with the pick-up lever atall times for prompt response to choke coil tension .

FAST IDLE CAM PULL-OFF FEATUR EA fast idle cam "pull-off ' feature is included on

some M4MC-M4MCA carburetor applications . Manifol dvacuum to the rear vacuum break diaphragm is suppliedthrough a water temperature controlled thermal vacuu mswitch (TVS) and by an electrically operated time dela ysolenoid .

During cold operation when manifold vacuum i sapplied through the TVS and the solenoid to the rea rvacuum break diaphragm, the diaphragm plunge rmoves inward pulling on the vacuum break rod whichrotates the vacuum break lever to "pull-off" the fastidle cam from the high step to the lower step setting .Thus, the cam "pull-off" feature prevents prolongedhigh idle speeds during the warm-up period .

FRONT VACUU MCHOKE

BREAK ADJUSTINGROD CHOKE / SCREW

FRONT VACUUM BREA KDIAPHRAG M

(DELAY UNIT USED O N-SOME MODELS )

NOTE: PLUNGE RBUCKING SPRIN GUSED ON SOME MODEL S

AI RVALV E

FILTERPURGE /-DIAPHR AG MFILTER . rrr~u ~PURGEL '

BLEED

~HOLE

INLET

'~

DELA YVALV E

CHECK SPRINGBALL

THERMOSTATI C

SECONDARYLOCKOU T

LEVE RFAST IDL E

CA MFOLLOWER

LATER 4MC CHOKE SYSTEM

FILTE R

PURGE/FILTER' ,,,,;

R ~! 1 ~rr}• DELAY

CHECK

VALVE/ .- .\\CHEC K

BALL

INLET

SPRINGM4MC & M4MCA CHOKE SYSTEM - TYPICA L

CHOKE CLOSING ~'~~ASSIST SPRING

►~

THERMOSTATI C- COIL U~\SECONDARY

LOCKOUT FAST IDLE INSIDE FAST IDLE

TANGLEVER

CAM

CUP ADJUSTIN GFOLLOWER BAFFLE SCRE W

FRONT VACUU MBREAK ADJUSTIN G

SCRE WFRONT VACUU M

BREA KDIAPHRAGM

9D. 5March 1981

Page 26

is adjusted at the factory . No attempt shouldbe made to adjust the Idle Load Compensa-tor unless, in diagnosis, curb idle speed isnot to factory specifications . If adjustmentis necessary, refer to Service Manual forproper procedures

MAJOR SERVICE OPERATIONS -ALL MODELS

Genera l

The procedures, below, apply to the complete over-haul with the carburetor removed from the engine .However, in many cases, service adjustments of indi-vidual systems may be completed without removingthe carburetor from the engine .

A complete carburetor overhaul includes disassembly ,thorough cleaning, inspection, replacement of all gas-kets — diaphragms — seals — worn or damaged parts ,and service adjustment of individual systems, plus re -storing tamper resistant features where applicable .

Disassembly, Cleaning, Inspection and AdjustmentsThe following disassembly and assembly procedures

may vary somewhat between applications due to specificdesign features. However, they will pertain basicall yto all Quadrajet models .

Figure 42 Typical Quadrajet Carbureto r

Disassembly

NOTICE : Before performing any service onthe carburetor, it is essential that the carbu-retor be placed on a holding fixture such a sBT-30-15. Without the use of the holdingfixture, it is possible to bend or nick throt-tle valves .

Idle Stop Solenoid Remova l1. Remove screw(s) securing the idle stop solenoi d

bracket to float bowl and remove solenoid and bracke tassembly . On some applications, the solenoid an dbracket assembly are an integral unit and serviced asa complete assembly. On some applications where thesolenoid is mounted in the bracket as a separate unit ,if solenoid replacement is necessary, bend back retainin gtabs on lockwasher; then remove large idle stop solenoidretaining nut and remove solenoid from bracket .

NOTICE : Follow the above procedure toremove the A/C idle speed solenoid,throttle closing dashpot, or throttle leveractuator . The idle stop solenoid, A/C idlespeed solenoid, throttle closing dashpot ,or throttle lever actuator should not be im-mersed in any type of carburetor cleane rand should always be removed before com-plete carburetor overhaul .

2. On 4MV models using either a Combinatio nEmission Control (C .E.C.) valve or idle stop solenoi dmounted on the carburetor :

a) On C.E.C. models only, remove vacuum hos efrom the C .E.C. valve and vacuum tube on the floatbowl .

b) Remove screw securing C .E.C. valve or idle stopsolenoid bracket to float bowl .

NOTICE : Do not remove the bracket forthe C.E.C. valve or idle stop solenoid fro mthe air horn assembly unless replacement o fthe bracket is necessary. If necessary to re-place the C .E.C . valve or idle stop solenoid ,follow procedure noted under Step 1, above .

Do not immerse the C .E.C. valve assemblyor idle stop solenoid in any type of carbu-retor cleaner .

AIR HORN REMOVAL1. If used, remove idle vent valve attaching screw ;

then remove idle vent valve assembly . If thermostaticvent valve is used, remove dust cover, then removevalve . Care should be used not to bend or distort th ebi-metal strip .

2. On those 4MV models using the vacuum operate dvent switch valve, remove small screw from top of ven tvalve plunger stem .

NOTICE : Hold plunger stem with needle -nosed pliers to prevent turning and tearingof diaphragm . Remove vent valve cover screwand air horn screw and carefully lift coverfrom air horn . Remove cover gasket, ven tvalve assembly, and spring, noting positionof the vent valve for later reassembly . Re -move diaphragm retainer and diaphrag mfrom the air horn by carefully moving th ediaphragm stem back and forth .

AIR HOR N

AIR VALV E

CHOKEVALVE

PUM PLEVE R

PUMPSTE M

TYPICAL QUADRAIET CARBURETOR

41

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9D-5March 198 1

Page 2 7

Figure 43 Removing Upper Choke Leve r

Figure 44 Pump Lever Remova l

3. Remove upper choke lever from the end of chokeshaft by removing retaining screw (Figure 43) . Then ,rotate lever to remove choke rod from slot in lever .

NOTICE : On models using a clip at theupper end of the choke rod, remove clipfrom rod and disconnect upper end of chokerod from choke shaft lever .

4. Remove choke rod from lower lever inside th efloat bowl casting .

NOTICE : Remove rod by holding lower leveroutward with small screwdriver and twistingrod counterclockwise .

5. With tool BT 7523 or equivalent, drive small rollpin (pump lever pivot pin) inward just enough unti lpump lever can be removed from air horn (Figure 44) .Then remove pump lever from pump rod . Note locatio nof rod (if in inner or outer hole) for later reassembly .

NOTICE : Do not remove roll pin completel yduring removal or disassembly of air horn .Use care in driving small roll pin to pre -

Figure 45 Secondary Metering Rod Remova l

vent damage to pump lever casting bosse sin air horn.

On those models that use a retaining clip inthe upper end of the pump rod, remove clipfrom upper end of the pump rod; then dis-connect pump rod from pump lever. Wirevent valve lever can be removed from pum plever if replacement is necessary .

Do not bend the pump rod to remove frompump lever ; follow the above procedures .

6. Remove secondary metering rods from secondaryorifice plates by removing small screw in the secondarymetering rod hanger (Figure 45) . Lift holder and rod sas an assembly straight up from the carburetor . Meteringrods may be disassembled from the hanger by rotatin gends out of the holes in the end of the hanger .

7. For early models with air valve dashpot, remove endof dashpot plunger rod from air valve lever . Some slideout of lever and others are held by a retaining clip . Thedashpot piston has a synthetic seal inside the pistonon the plunger shaft .

NOTICE : The seal should not be immersedin carburetor cleaner as the seal will bedestroyed .

8. Remove air horn to bowl attaching screws (Figure46); early models have 9 screws, later models have 1 3screws for better control of evaporative emissions . Ifused, remove bowl vent valve cover, spring and gasketfrom beneath front air horn screw .

9. If used, remove idle vent valve attaching screw ; thenremove idle vent valve assembly . If thermostatic ventvalve is used, remove dust cover, then remove valve .Care should be used not to bend or distort the bi-meta lstrip .

On those 4MV models using the vacuum operatedvent switch valve, remove small screw from top of ven tvalve plunger stem .

9D.5

March 198 1

Page 28

Figure 46 Air Horn Screw Remova l

NOTICE : Some models have a secondarybaffle plate mounted under the (2) cente rair horn attaching screws next to the secon-dary bores (Nos . 3 and 4). The baffle canbe removed also at this time . Other model shave a secondary air valve lockout shiel dlocated over the lockout lever . This is hel din place by the air horn screw next to thelockout lever and a small attaching screw .(Check the "C" parts bulletin in the Delc oCarburetor Parts and Service Manual 9X forcorrect usage of these parts) .

10. Remove air horn from float bowl by lifting straightup (Figure 47) . On 4MV-4MC models, rotate air horn toremove vacuum break rod from dashpot lever on end ofthe air valve shaft . Air horn gasket should remain onbowl for removal later .

NOTICE: Place air horn inverted on cleanbench . When removing air horn from floatbowl, use care to prevent bending the smalltubes protruding from the air horn . Thesetubes are permanently pressed into the airhorn casting . DO NOT REMOVE .

11. If not removed previously, remove front vacuu mbreak hose . Then remove vacuum break control an dbracket assembly . The diaphragm assembly may no wbe removed from the air valve dashpot rod and thedashpot rod from the air valve lever .

12. For later models that use a pump plunger ste mseal (Figure 48), remove seal by inverting air horn anduse Tool BT-7954 or equivalent to remove seal retainerring. Discard retainer and seal .

NOTICE : Use care in removing the pum pplunger stem seal retainer to prevent damageto air horn casting. A new seal and retaine rare required for reassembly .

Further disassembly of the air horn is not re-quired for cleaning purposes .

Figure 47 Air Horn Remova l

Figure 48 Pump Plunger Stem Sea l

AIR HORN DISASSEMBL YIf part replacement is required, proceed as follows :

NOTICE : On "modified" models using thebowl vent valve, the bowl vent valve andactuating arm are permanently retained inthe air horn . DO NOT REMOVE.

1. Remove staking on (2) choke valve attaching screws ;then remove choke valve screws, valve, and shaft fro mair horn .

2. If the air horn is equipped with an air valve lock -out lever and it needs replacement, remove the lockou tlever by driving out roll pin with small drift punch .

NOTICE : Air valves and air valve shaftshould not be removed . However, if it isnecessary to replace the air valve closin gspring or center plastic eccentric cam, a re -pair kit is available . Refer to the "C" Parts

L./

9D- 5March 198 1

Page 29

Figure 49 Pump Remova l

Figure 50 Auxiliary Power Piston Metering Ro dRemova l

Bulletin in the Delco Carburetor Parts andService Manual (9X) for part number applica-tion .

Instructions for assembly are included in th erepair kit .

FLOAT BOWL DISASSEMBLY1. Carefully lift corner of air horn gasket and remove

pump plunger from pump well (Figure 49) .

NOTICE : On "modified" models, carefullyloosen air horn gasket and lift one corner toremove pump plunger from pump well .

2. If used, remove bowl vent valve spacer from pumpplunger stem .

3. Remove air horn gasket from dowels on secondary

Figure 51 Power Piston Assemblie s

side of bowl ; then remove gasket from around the mai npower piston and attached primary metering rods bylifting tab of gasket from beneath the hanger (beingcareful not to distort the small springs that hold themetering rods in place) and lift gasket from the bowl .

4. For models that have an auxiliary (front) powe rpiston (as shown in Figure 50), hold auxiliary powe rpiston and swing hanger toward front of carbureto rwhile at the same time pushing rearward on meteringrod and compressing rod spring retainer until groove i nrod aligns with slot in hanger . Then remove rod by liftingit up and out of the fixed metering jet . Hold main (rear)primary power piston down and swing auxiliary (front )power piston hanger rearward until it touches the pri-mary power piston — then release the primary pisto nand remove air horn gasket per step 3 above .

5. Remove pump return spring from pump well .

6. Remove main power piston and metering rods asan assembly. There are four different types of power pis -ton retainers used (Figure 51) .

a. The first design has a "button head" pin extensio npressed into the base of the power piston . This typepower piston is held in place by the "button head "which protrudes through a hole in the throttle bod ygasket. The power piston can be removed by usin gneedle-nosed pliers to pull straight up on metering ro dhanger directly over power piston .

b. The second type power piston retainer is a fla tbrass spring clip which fits around the power piston ,at the center . This type power piston assembly is re -moved in the same manner as above .

"

~+►"

ai AUXILIAR Y

f '._

POWER PISTO N

AUXILIARY POWER PISTON METERIN G ROD REMOVALL

FLOAT NEEDL EPULL CLI P

FLOATRETAINING

PIN

FLOATASSEMBLY

POWER PISTONAND PRIMARY

METERING RODS

FUEL INLET NU TSAND FILTER

9D-5March 1981

Page 30

Delco

Figure 52 Power Piston-Metering Rod Assembl y

c. The third type power piston retainer is a springclip which fits over and around the top of the powe rpiston cavity . Two fingers at the top of the clip hold thepiston down in the cavity . This type power piston canbe removed by pushing upward on the clip retaine rto disengage it from the casting .

d. The fourth power piston retainer is a plastic re-tainer which is part of the power piston assembly . Theplastic retainer fits in a recess at the top of the powerpiston cavity. The power piston with the plastic retaine rcan be removed by pushing the piston downward againstspring tension and allowing it to snap back against theretainer . Repeat this snap back action until it "pops"out of casting . This procedure may have to be repeate dseveral times to free the power piston retainer . Do no tattempt to remove this type power piston by using plier son metering rod hanger, as irreparable damage to th episton assembly may be caused .

7. Remove metering rods from main power pisto nhanger by disconnecting tension spring loop from to pof each rod (Figure 52); then, rotate rod to remove fromhanger .

NOTICE : Use care when disassembling rod sto prevent distortion of tension spring and/ormetering rods . Note carefully position oftension spring for later reassembly .

8. Remove the power piston spring(s) from the well .

9. If used, remove auxiliary (front) power pisto nby depressing piston stem and allowing it to snap free

(following procedure noted in Step 6d, above) . Removeauxiliary power piston spring from the well .

NOTICE : The main (rear) and auxiliary(front) power piston springs must NOT beinterchanged . To prevent mixing of springs ,lightly wrap a piece of masking tape aroundthe auxiliary power piston spring for identi-fication. The auxiliary (front) power pistonspring is the longer of the two springs .

10 . Remove plastic filler block over float valve .11 . Remove float assembly and float needle by pulling

up on hinge pin .

12 . Remove inlet needle seat and gasket using Too lBT-3006M or wide blade screwdriver .

NOTICE : Float needle and seat are factorymatched and tested and should be replace donly as a set .

For diaphragm type float assemblies (earl ymodels) :

a. Remove float assembly by pulling upward on hingepin until pin can be removed from float hanger b ysliding toward pump well . After pin is removed, slidefloat assembly toward front of bowl to disengage needl epull clip from float arm . Do not distort float needl epull clip .

b. Using needle-nosed pliers, remove pull clip fro mfloat needle .

c. Remove two screws from float needle diaphrag mretainer ; then remove retainer and float valve assemblyfrom bowl .

NOTICE : Valve seat is factory staked andtested. Do not attempt to remove or restake.If damaged, replace float bowl assembly .

APT METERING ROD - WIT HANEROID OR FILLER SPOO L

13. On later "modified " models that use the AP T(adjustable part throttle) metering rod assembly withaneroid or filler spool, remove two cover screws andcarefully lift the metering rod assembly from the floa tbowl cavity (Figure 53) .

NOTICE : The APT metering rod assembly ,with aneroid or filler spool, is extremelyfragile . Use care in handling these criticalparts . Do not immerse aneroid or filler spoo lin carburetor cleaner . The APT metering rodassembly is pre-set at the factory and N Oattempt should be made to readjust in th efield. If replacement is necessary, see APTMetering Rod Replacement (Step 7a ,page 38) .

14 . Many models have a simple blank insert installe din the aneroid bowl cavity (Figure 53) . Remove insert .

POWER PISTON & METERING RO DASSEMBLY-TYPICAL

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Delco

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Figure 53 Modified APT Devices

NOTICE: On M4MC-M4ME models thathave an APT Metering Rod Adjustmentscrew in the float bowl (located in a wel lnext to the main power piston), the scre wis pre-set at the factory and no attemp tshould be made to change this adjustmentin Service. If float bowl replacement isrequired for service, the new bowl assemblywill be supplied with the APT meterin gscrew pre-set as required .

15. Remove main metering jets only if necessary(Figure 54) .

NOTICE : No attempt should be made to re-move the auxiliary (front) power pistonmetering jet, APT metering jet, or secondarymetering orifice plates . Normal cleaning i sall that is necessary . These jets are fixed and,if damaged, float bowl replacement is re-quired .

16. Using a screwdriver, remove pump discharg echeck ball retainer, then steel check ball (Figure 54) .

17. If used, remove baffle from side of pump wel lfill slot .

18. The baffle plate in the secondary bores need notbe removed for cleaning purposes . If replacement isnecessary, remove plate by lifting upward out of slot sin side of bores .

19. CHOKE MECHANISM DISASSEMBL Y

A. Vacuum Break Removal

1 . Remove vacuum break hose from main vacuu mbreak assembly and, if used, from rear (or auxiliary)

Figure 54 M4MC-M4ME "Modified" Float Bowl -Typica l

Figure 55 Vacuum Break and Fas tIdle Cam - Early Models

vacuum break assembly, and remove hose(s) from con-nection on float bowl .

2. Remove retaining screw from choke vacuum breakbracket assembly and remove assembly from float bowl .If not removed previously, vacuum break rod can no wbe removed from the main vacuum break plunger b yrotating rod out of plunger stem (Figure 55) .

3. Remove secondary lockout lever, or idle speed-u plever (where used), from projection on bowl casting .

4. Remove the fast idle cam from bushing on chokevacuum break bracket assembly .

NOTICE : If further disassembly of the choke

TYPICAL (`MODIFIED') FLOAT BOWL

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Delco

Figure 56 Secondary Vacuum Break Remova l

mechanism is necessary, the vacuum brea kassemblies can be removed as follows :

.a) (Early Models) Remove clip on connecting link a tvacuum break lever . Then, remove link from lever andvacuum break diaphragm plunger .

b) Some models have vacuum break units attache dto the brackets by retaining ears which are bent togetherto hold the diaphragm assembly . Where found, the re-taining ears must be spread to unclamp either the pri-mary (front) or secondary (rear) vacuum break assembly.

c) Late models have integral vacuum break diaphragm -bracket assemblies . Remove attaching screws holdingunits to float bowl . The secondary vacuum break assem-bly has a rod connecting the plunger to the intermediatechoke shaft lever . This can also be removed by rotatingthe vacuum break diaphragm assembly by sliding th erod out of the plunger stem and the other end out ofthe vacuum break lever (See Figure 56) .

NOTICE : Do not place vacuum break unit sin carburetor cleaner .

B. Choke Disassembly (Early Models )

1. Remove three attaching screws and retainers fromchoke cover and coil assembly . Then pull straight out -ward to remove cover and coil assembly from chokehousing. Remove choke cover gasket if used .

NOTICE : A cover scribe mark is locatedrelative to the index marks cast into thechoke housing . The cover position should b enoted at time of disassembly so that coverindexing can be restored upon reassembly .

NOTICE : It is not necessary to remove baffleplate from beneath the thermostatic coil onhot air choke models . Distortion of th ethermostatic coil may result if forced off th ecenter retaining post on the choke cover .

2. Remove choke housing assembly from float bowl

Figure 57 Choke Housing Remova l

by removing retaining screw and washer inside the chokehousing (Figure 57) . The complete choke assembl ycan be removed from the float bowl by sliding outward .

3. Remove lower choke lever from inside float bowlcavity by inverting bowl .

4. Remove plastic tube seal from choke housing i fused .

NOTICE : Plastic tube seal should not b eimmersed in carburetor cleaner .

5. To disassemble intermediate choke shaft fromchoke housing, remove coil lever retainer screw . Thenremove lever from flats on intermediate choke shaft .Remove intermediate shaft from the choke housing bysliding outward . The fast idle cam can now be removedfrom the intermediate choke shaft .

6. Remove the cup seal from inside choke housingshaft hole if the housing is to be immersed in carbu-retor cleaner. Also, remove cup seal from the floa tbowl insert for bowl cleaning purposes (Figure 58) .

NOTICE : Do not attempt to remove bowlinsert .

C. Choke Disassembly (Late Models )

Late model carburetors have a tamper resistant chok ecover locating and retention method . Cover and coi lassembly retainer screws (early models) have been re -placed by rivets to discourage choke readjustment inthe field. Should it be necessary to remove the cove rand coil assembly or choke housing for cleaning, over -haul or replacement, proceed as follows :

CHOKE COVER REMOVA L1. Support float bowl and throttle body as an assembl y

on a suitable holding fixture such as tool BT-30-15 .

2. Carefully align a #21 drill ( .159") on rivet hea dand drill enough to remove the three rivet heads (Figur e59) and then, using a drift and small hammer, drivethe remainder of the rivets out of the choke housing .

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NOTICE : On tamper resistant models aspecial cut-out is notched in the choke coverwhich is aligned with an extended tab onone cover retainer which is located at the2 o'clock position . This is a locating methodthat properly indexes the cover and coilassembly within the choke housing .

3. Remove choke cover and coil assembly from chok ehousing . Remove choke cover gasket, if used ; also re-move inside baffle plate, if used .

4. Remove choke housing assembly from float bowlusing procedures described previously for early models .

DISASSEMBLY OF REMAININGFLOAT BOWL PART S

1 . If used, remove hot idle compensator by removing

(2) screws in compensator cover at rear of float bowl .Remove cover, hot idle compensator, and "0" ringseal in bowl cavity recess beneath compensator .

Some models have the hot idle compensator located ad -jacent to the pump well area . Remove hot idle compen-sator assembly and cork "0" ring .

NOTICE: Hot idle compensator "0" ringseal is to be replaced with a new seal attime of reassembly.

2. Remove fuel inlet nut, gasket, filter assembly andspring (Figure 60) . Some models use a fuel strainer inplace of a filter and spring . Consult the parts list foreach model for proper parts application .

3. Invert float bowl - throttle body assembly and placeon a clean flat surface . Remove throttle body by re -moving throttle body to bowl attaching screws (Figur e61) . Lift throttle body from bowl .

4. Remove throttle body to bowl insulator gasket .

Figure 60 Fuel Filter Assembly - Typica l

Figure 61 Throttle Body Remova l

SEAL -INTERMEDIATECHOKE SHAF TIN FLOAT BOW L

LEVER - SECONDAR YLOCKOU T

(OUADRAJET ONLY)

SEAL - INTERMEDIATE CHOKESHAFT IN CHOKE HOUSIN G(HOT AIR CHOKES ONLY )

SCREW - CHOK EHOUSING ATTAC H

Figure 58 Choke Assembly - Typica l

Figure 59 Choke Cover Removal - Late Models

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THROTTLE BODY DISASSEMBLYNOTICE : Place throttle body assemblyon carburetor holding fixture to protectthrottle valves . Extreme care must be takento avoid damaging throttle valves .

1. Remove pump rod from throttle lever by rotatingrod out of primary throttle lever .

2. Further disassembly of the throttle body is no trequired for cleaning purposes . The throttle valve screwsare permanently staked in place and should not b eremoved . The throttle body is serviced as a complet eassembly .

NOTICE: Do not remove the steel plugs thatcover the idle mixture needles (late models )or the plastic limiter caps that are found o nsome models . These devices are installed toprotect critical factory settings and to meetemissions control regulations . If proble mdiagnosis indicates that the carburetor is atfault relative to a driver complaint, an emis-sions failure, or if normal soaking and ai rpressure fails to clean the idle passages, orif idle needle or throttle body replacement isrequired, only then may the plugs or limitercaps be removed in order to perform necessaryservice .

If plug removal is required to replace idle needle sor to perform necessary adjustments, proceed as follow s(Figure 62) :

a. Make two parallel cuts in the throttle body betweenthe locator points beneath the idle mixture needle plugswith a hack saw (Step 1) . The cuts should reac hdown to the steel plug but should not extend more tha n1/8" beyond the locator points . The distance betweenthe saw marks depends on the size of the punch t obe used .

b. Place a flat punch at a point near the ends of thesaw marks in the throttle body. Holding the punch at a45° angle, drive it into the throttle body until the cast-ing breaks away, exposing the steel plug (Step 2) .

c. Holding a center punch vertical, drive it into thesteel plug. Then, holding the punch at a 45° angle ,drive the plug out of the casting.

NOTICE: Hardened plug will break rathe rthan remaining intact . It is not necessaryto remove the plug completely; instead ,remove loose pieces to allow use of idle mix-ture adjusting tool J-29030 or BT-7610B (o requivalent) .

d. Using Tool J-29030, or BT-7610B, adjust idlemixture needle according to specifications . If the idlemixture needles are removed, readjust the idle mixtureper recommended instructions furnished by the vehiclemanufacturer or provided in AC-Delco Service BulletinsSD-100, SD100A or 9D-1978A .

Figure 62 Idle Mixture Plug Remova l

NOTICE: Before removing the idle mixtureneedle, it is suggested that the old needle b elightly bottomed and the number of turns tobottom be recorded . Then, when installingthe new needle, lightly bottom, then backoff the number of turns it took to bottomthe old needle . Proceed to adjust needles tofinal idle mixture following procedures an dspecifications .NOTICE: After idle mixture adjustment iscomplete on models where plugs were re -moved, it is advised that the needle settingsbe sealed with a silicone sealant RTV rubberor equivalent to prevent fuel vapor loss . Ifnecessary to remove the idle mixture needle swith idle limiter caps, destroy the limite rcaps . Do not install a replacement cap as abare mixture screw is sufficient evidence toindicate that the mixture has been readjusted .

CLEANING AND INSPECTIO N1 . Thoroughly clean carburetor castings and metal

parts in an approved carburetor cleaner, such as CarbonX (X-55) or its equivalent .

NOTICE: The following should NOT b eimmersed in carburetor cleaner as they wil lswell, harden, or distort :

A. The electric choke, any rubber parts, electricsolenoid, plastic parts, diaphragms, pump plunger ,aneroid, filler spool, or aneroid cavity inser t

B. Vacuum Break Assemblie sC. Choke housing plastic tube seal or gasketD. Choke coil and cover assemblyE. Intermediate choke lever shaft cup seal recessed

in float bowl insert

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F. If choke housing is to be immersed in carburetorcleaner, remove the cup seal from inside the chok ehousing shaft hole

G. Fuel filter assembly, and check valve (if used )

H. Idle stop solenoid, A/C idle speed solenoid ,throttle closing dashpot, throttle lever actuator, C.E.C.solenoid .

The plastic cam on the air valve shaft will withstan dnormal cleaning in carburetor cleaner (rinse thoroughl yafter cleaning) .

Do not attempt to remove bowl insert . The bushingwill withstand normal cleaning . (Rinse thoroughly aftercleaning) .

2. Thoroughly clean all metal parts and blow dry withshop air. Make sure all fuel passages and meteringparts are free of burrs and dirt . Do not pass drills orwire through jets and passages .

3. Inspect upper and lower surface of carbureto rcastings for damage.

4. Inspect holes in levers for excessive wear or out ofround conditions . If worn, levers should be replaced .

5. Check, repair, or replace parts if the followingproblems are encountered :

A. Flooding

1. Inspect float needle and seat for dirt, deep weargrooves, scores, and proper seating. (Needle and seatchecking tool BT-6513 may be used to check the sea lof the standard type needle in the seat) .

NOTICE: When checking the rubber tippedneedle, do not exceed 3" of vacuum for sixseconds to prevent distortion of the rubber tip .

2. Inspect float needle pull clip for proper installation .Be careful not to bend needle pull clip .

3. Inspect float, float arms and hinge pin for dis-tortion, binds, and burrs . Check density of material inthe float ; if heavier than normal, replace float .

4. Clean or replace fuel inlet strainer or filter .

B. Hesitation

1. Inspect pump plunger for cracks, scores, or exces-sive cup wear .

2. Inspect pump duration and return springs for beingweak or distorted .

3. Check all pump passages and jets for dirt, im-proper seating inlet or discharge balls, scores in pumpwell .

4. Check pump linkage for excessive wear, repairor replace as necessary .

C. Hard Starting-Poor Cold Operatio n

1. Inspect inlet needle for sticking, dirt, etc .

2. Examine fast idle cam for wear or damage .

3. Also check items under "Flooding" .

D. Poor Performance - Poor Gas Mileag e

1. Clean all fuel and vacuum passages in castings .

2. Check choke valve for freedom of movement .

3. Inspect power piston(s), metering rods and jets fo rdirt, sticking, binding, damaged parts or excessive wear .

4. Check air valve for binding condition . If air valveis damaged, the air horn assembly must be replaced .A torsion spring kit is available for repairs to the ai rvalve closing spring . A new plastic eccentric cam isincluded in the kit .

E. Rough Idl e

1. Inspect gasket mating surfaces on castings fo rdamage to sealing beads, nicks or burrs .

2. Clean all idle fuel passages.

3. Check throttle lever and valves for binds, nicksand other damage .

4. If removed, inspect mixture needles for ridges, burrs ,or being bent . Install idle mixture needles and spring suntil needles are lightly seated . Back out mixture needlesspecified number of turns as an initial adjustment .

NOTICE: Final idle mixture and idle spee dsettings should be made on the car followingthe vehicle manufacturer's procedures andspecifications noted in the service manual orAC-Delco Service Bulletins SD-100, SD-100A ,or 9D-1978A .

5. Check all diaphragms for possible ruptures or leaks .

6. Clean plastic parts only in cleaning solvent - neve rin gasoline .

CARBURETOR ASSEMBLYThrottle Body Reassembly

1. If removed, install fast idle cam follower, fast idl elever on end of primary throttle shaft . Install torsionspring (where used) and retaining screw in end of shaft .Tighten securely.

2. If removed, install idle mixture needles and springsuntil lightly seated . Then, as a preliminary idle mixtureadjustment, back out the mixture needles number o fturns counted at time of disassembly (see step 2, Pag e34), or back out mixture needles number of turns speci-fied by the vehicle manufacturer . Final adjustmentmust be made on the engine using the procedures andspecifications of the vehicle manufacturer .

NOTICE: Do not force the idle mixtureneedle against the seat or damage will result .

3. Install lower end of pump rod in throttle leverby aligning tang on rod with slot in lever. End of rodshould point outward toward throttle lever .

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Float Bowl Reassembly (Refer to Figures 49 through 60 )1. Install new throttle body to bowl insulator gaske t

making sure the gasket is properly positioned on tw olocating dowels on bottom of float bowl .

2. Install throttle body on bowl making certain throttlebody is properly located over dowels on float bowl ;then install throttle body to bowl screws (and lockwashers,if used) and tighten evenly and securely .

NOTICE: If a new (service) throttle body isused on 4MV-4MC models, be sure to per -form APT setting procedures as describedon page 42. Place carburetor on prope rholding fixture (such as BT-30-15) .

3. Install fuel inlet strainer, or filter (and check valve ,if used), spring, new gasket and inlet nut . Tightennut securely (18 ft . lbs .) . The filter spring is not use don models that have a fuel strainer .

NOTICE: When installing a service replace-ment filter, make sure the filter is the typethat includes the check valve, if required, t omeet government safety standards . New ser-vice replacement filters with check valve meetthis requirement. When properly installed ,hole in filter faces toward inlet nut . Ribs onclosed end of filter element prevent filte rfrom being installed incorrectly unless forced .Tightening beyond specified torque ca ndamage nylon gasket.

4. If used, install hot idle compensator "0" ringseal in recess in bowl, then install hot idle compensator .Install compensator cover and (2) retaining screws .Tighten screws securely.

NOTICE: On those models having the com-pensator located in the float bowl adjacen tto the pump well area, install "0" ringcork seal and hot idle compensator in cavit yin float bowl .

4MV Choke Assembly

5. If the vacuum break diaphragm (s) was remove dfrom the bracket, slide vacuum break diaphragm be-tween retaining ears and bend ears down slightly t ohold securely . .

NOTICE: If a second (auxiliary) vacuu mbreak diaphragm is used, the vacuum dia-phragm rod must be installed in the vacuu mbreak lever and plunger stem prior toinstalling the unit on the choke bracket .

Early Models

Install vacuum break link (U-bend end) in slot indiaphragm plunger . End of link should be on insid eof slot toward choke bracket . Install other end of vacuumbeak link in hole on vacuum break lever and retai nwith clip .

6. Install the secondary lockout lever (or idle speed -up lever, if used,) on the bearing pin on the float bowl .

7. Install fast idle cam on the choke shaft makingsure the cam actuating tang on the intermediate chokeshaft lever is located on the underside of the tail o fthe fast idle cam, or in slot of fast idle cam .Assembly of Choke Housing to Float Bowl

1. If used, install new cup seal into insert on sid eof float bowl for intermediate choke shaft. Lip on cu pseal faces outward .

2. Install secondary throttle valve lockout lever (i fused) on boss on float bowl with recess in hole i nlever facing inward (Figure 63) .

Figure 63 Assembly of Choke Housing to Floa tBowl

3. If used, install new cup seal into inside chokehousing shaft hole . Lip on seal faces inward, towar dfloat bowl .

4. Install fast idle cam onto the intermediate chokeshaft (steps on fast idle cam face downward) .

5. Except on early 4MC models, carefully install fas tidle cam and intermediate choke shaft assembly throug hseal in choke housing; then install thermostatic coillever onto flats on intermediate choke shaft . The thermo-static choke coil lever is properly aligned when bothinside and outside levers face toward fuel inlet . Instal linside lever retaining screw into end of intermediatechoke shaft . Tighten screw securely.

6. Install choke rod (plain end) into hole in lowe rchoke rod inner lever; then holding choke rod withlower end pointing outward, lower choke rod innerlever into cavity in float bowl . Install plastic tube seal(if used) into cavity on choke housing before assemblin gchoke housing to bowl . On early 4MC models withvacuum diaphragm unit integral with choke housing ,install small gasket on vacuum passage between choke

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housing and float bowl . Install choke housing to bowlsliding intermediate choke shaft into lower choke inne rlever .

NOTICE: Tool BT-6911 can be used to holdthe lower choke rod inner lever in correc tposition while installing the choke housingas shown in Figure 64 .

7 . Install choke housing retaining screw and washerand tighten securely .

NOTICE : The intermediate choke shaft leve rand fast idle cam are in correct relationwhen the tang on lever is beneath the fastidle cam. Do not install choke cover and coilassembly until inside coil lever is adjusted(see Adjustment Procedures Bulletin 9D-5 Aof the Delco Parts and Service Manual 9X) .

COMPLETION OF FLOAT BOWLASSEMBLY - ALL MODELS

NOTICE : Steps 1 and 2 pertain only toM4MC-M4ME units that use a rear vacuumbreak assembly .

1. Holding down on fast idle cam (hot idle position) ,install end of rear vacuum break rod in hole in inter -mediate choke lever .

2. Install end of vacuum break rod in slot in rearvacuum break plunger . Then install rear vacuum brea kand bracket assembly to float bowl using two attachingscrews. Tighten securely .

NOTICE: Do not attach vacuum break hoseuntil after the rear vacuum break adjust-ment is completed .

3. If removed, install baffle in secondary side offloat bowl with notches toward top of bowl . Make surebaffle is seated and top is flush with casting surface .

4. On M4MC-M4ME models, install baffle insid epump well with slot toward bottom .

5. Install pump discharge ball and retainer in passagenext to pump well . Tighten retainer securely .

6. Install primary main metering jets, if removed .TIGHTEN SECURELY .

7. On "modified" models that use an APT meterin grod assembly with aneroid or filler spool, install meteringrod assembly into float bowl, carefully aligning meteringrod tip with hole in fixed jet . Tab on cover goes in slotin float bowl closest to the fuel inlet nut (Figure 66) .

Figure 65 Float Bowl - Typica l

Figure 66 APT Metering Rod Replacemen t

TYPICAL ('MODIFIED') FLOAT BOW L

Figure 64 Installing Lower Choke Rod Lever

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NOTICE: The position of the APT meterin grod, with aneroid or filler spool, in the fixe djet is extremely critical . Adjustment shoul dNEVER be attempted unless replacement o fthe APT metering rod assembly is require ddue to damage to the rod, or failure of th eoriginal aneroid .

If required, the threaded metering rod assembl ymay be replaced as follows :

a. Note position of slot in adjusting screw of meteringrod assembly and lightly scribe mark on cover .

b. With cover screws removed, carefully lift th emetering rod and cover assembly from the float bowl .

NOTICE: DO NOT immerse the aneroid orfiller spool in carburetor cleaner . The meter-ing rod assembly, with aneroid or filler spool ,is extremely fragile . Use care in handlin gthese critical parts .

c. With metering rod and cover assembly held up -right, using a small screwdriver, turn the adjustingscrew counterclockwise, carefully counting the numberof turns until the threaded metering rod assembly bot-toms in the cover. Record number of turns counte dfor later reference (see Step f) .

d. Remove "E" clip retainer from threaded end ofrod . Then using small screwdriver, turn slotted rod clock -wise until rod assembly disengages from cover .

NOTICE : Rod assembly is spring-loaded .Use care in removing rod assembly from cover.

e. Install tension spring on replacement metering rodassembly and thread rod and spring assembly int ocover until the rod assembly bottoms in cover .

f. Using a small screwdriver, turn the adjustin gscrew clockwise until the rod is backed out of the coverexactly the same number of turns from scribe line asrecorded during disassembly (see Step c) .

NOTICE: When properly adjusted as above ,slot in replacement AFT metering rod assem-bly may not line up with scribe mark on cover .

g. Install "E" clip in groove in rod assembly, makingsure clip is locked securely in place .

h. Carefully install cover and metering rod assembl yonto float bowl aligning tab on cover assembly wit hslot in float bowl closest to the fuel inlet nut, (Figure 66) .

NOTICE: Use care installing the meteringrod and cover assembly into float bowl t oprevent damaging or bending the meterin grod tip .

i. Install cover attaching screws and tighten securely .

8 . On other "modified" models that do not use theAPT metering rod assembly with aneroid or filler spool ,install aneroid cavity insert into float bowl .

Figure 67 Float Needle Pull Clip Locatio n

9. Install needle seat, with gasket, using tool BT-3006M .

10. To make float adjustment easier, carefully ben dfloat arm upward at notch in arm before assembly .

11. Install needle by sliding float lever under pul lclip from front to back . Correct installation of the needl epull clip is to hook the clip over edge of the float on thefloat arm facing the float pontoon (Figure 67) . Withfloat lever in pull clip, hold float assembly at toe andinstall hinge pin from pump well side (ends of hing epin face the accelerating pump well) .

NOTICE : Do not install float needle pul lclip into holes in float arm . Severe floodingwill result .

12. Install float needle and diaphragm assembly ,making sure diaphragm is properly seated .

13. Install diaphragm retainer and two screws . Tightensecurely .

14. Install float needle pull clip on float needle stemusing needle nosed pliers. Pull clip is properly positionedwith open end toward front of bowl .

15. Install float by sliding float lever into loop inpull clip . With lever in clip, hold float assembly a ttoe and install float hinge pin from pump well side .Be careful not to bend needle pull clip .

NOTICE : If desired, certain Quadrajetmodels may be converted from the diaphrag mtype needle and seat to the standard or con-ventional float needle and seat by installinga service modification kit . (Refer to 9C PartsSection of the Delco 9X Manual for specifi capplications and part number )

16. Carefully adjust float level following proceduresand specifications listed in the vehicle manufacturer ' sservice manual or in the "D" section of the Delco Carbu-retor Parts and Service Manual (9X) .

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17. On M4MC-M4ME models, install plastic fille rblock over float needle, pressing downward until properl yseated .

18 . Install power piston spring in power piston well .NOTICE : If two power piston springs areused, the smaller spring seats in the cente rof the piston and bottoms on the float bow lcasting . The larger diameter spring surround sthe small inner spring to exert additiona lpressure on the bottom of the power piston .

19. If primary metering rods were removed fromhanger, reinstall making sure tension spring is connecte dto top of each rod (see Figures 52 or 68) .

20. Install power piston assembly in well with meterin g.rods carefully positioned in metering jets .

NOTICE :a) On those models that have a "Butto nHead" pin extension pressed into the bas eof the power piston, press down firmly toinsure engagement of retaining pin in throttlebody gasket .b) Some models use a spring clip over top ofpower piston well . On these, make sure clipis installed and seated .c) On those which have a split ring retaineraround the center of the power piston, care-fully compress split ring and push pistondown in well until it seats . This properlypositions this type retainer .On late models which use the plastic re-tainer on the top of the power piston (a sshown Figure 68),install power piston in wel land press down firmly on the plastic retainerforcing it into the recess in the bowl . Makesure it is properly seated . It may be necessaryto tap the plastic retainer lightly in plac ewith a hammer and drift . When installedcorrectly the plastic retainer is flush with thetop of the float bowl casting .

21 . On "modified" models with dual power pistons ,remove masking tape, used for identification, and installauxiliary power piston spring in power piston well (frontlocation — long spring) .

Install auxiliary power piston assembly without meter-ing rod in front well . Press down firmly on plastic powerpiston retainer to make sure the retainer is seated i nrecess in bowl and that the top is flush with the top o fthe float bowl casting . If necessary, using a drift punchand small hammer, tap retainer lightly in place .

22 . On 4MV-4MC models, install plastic filler blockover float needle, pressing downward until properlyseated.

23 . Install accelerator pump return spring in pumpwell .

Figure 68 Power Piston Installatio n

24. On dual power piston models, hold main (rear)power piston down and swing auxiliary (front) powe rpiston rearward until it touches the main power piston.Then release main power piston .

25. Install air horn gasket by carefully sliding tab o fgasket around metering rods and beneath the powerpiston hanger . Position gasket over the two dowel pin son the float bowl .

NOTICE : Air horn gaskets for "modified"Quadrajet models differ in that some havean extra hole forward of the main meterin grod hanger, either for the auxiliary hange r(dual power piston models) or for the AP Tadjustment screw (Fig . 69) . Be sure to usethe correct gasket for the carburetor beingworked on .

26. On dual power piston models, hold main (rear)power piston down and swing auxiliary power pistontoward front of carburetor . Release main power piston .

Holding auxiliary power piston down with hange rtoward front of carburetor, carefully insert the auxiliarymetering rod in the fixed jet . Using finger to compressspring toward end of rod, slide rod onto small diamete rgroove in hanger and release spring . Correct springlocation is on front side of hanger facing fuel inlet nut(Fig . 50) . The hanger, when properly installed, willpoint toward rear of the metering rod cover (with aneroidor filler spool) .

27. 4MV-4MC models — install accelerator pumpplunger in pump well . M4MC-M4ME models — if used,install bowl vent valve spacer on accelerator pum pplunger stem . Carefully lift corner of the air horngasket and install accelerator pump plunger in the pumpwell by pushing the plunger to the bottom of the wel lagainst return spring force . While holding in thi sposition, align pump plunger stem with hole in gasketand press gasket into place (Figure 69) .

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Figure 69 Installing Air Horn

AIR HORN REASSEMBLY1 . Install the following, if removed :

a) Pump stem seal and retainer .

b) Choke shaft, choke valve and (2) attaching screws .Tighten screws securely in place .

c) Dashpot plunger rod through air horn and attache dto air valve dashpot lever . Make sure clip retainer isinstalled (where used) .

d) Air valve lockout lever (if used) - retain with rollpin . Make sure lever is free from binds .

e) Normally, the air valve and shaft do not have tobe removed from the air horn for cleaning purposes . Arepair kit is available which includes a new plastic cam ,an air valve torsion spring, and retaining pin . Completeinstructions for installation also are included in the kit .(Refer to the "C" Parts Bulletin in the Delco Carbu-retor Parts and Service Manual for part number appli-cation) .

If it was necessary to replace the air valve closin gspring and the air valve shaft was removed, install ai rvalve shaft, plastic cam, air valves and four (4) attachingscrews . Center air valves, tighten screws and stake inplace . Make sure air valve operates freely with no binds .Then install air valve closing spring in air horn cavity .Insert spring pin, adjust pin, adjust air valve closingspring as outlined under adjustment procedures .

AIR HORN TO BOWL INSTALLATIO N1 . 4MV-4MC models - Carefully lower air horn as-

sembly onto float bowl, aligning bleed tubes, pull-over

enrichment tubes (if used), and accelerating well tube swith proper holes hi gasket, and positioning pump plungerstem through hole in air horn.

On 4MV models using a "clipless" vacuum breakrod, install vacuum break rod into main (front) vacuumbreak diaphragm plunger and into air valve lever onair horn before the air horn is lowered onto the floatbowl .

Position pump plunger stem in air horn and dashpot(where used) in well in float bowl . Gently lower ai rhorn assembly on gasket on float bowl, locating dowel sthrough gasket until properly seated.

2. M4MC-M4ME Model s

Carefully lower air horn assembly onto float bowl(holding down on air horn gasket at pump plungerlocation), making sure that the bleed tubes, pull-ove renrichment tubes (if used), and pump plunger stem arepositioned properly through the holes in the air horngasket (Figure 69) .

NOTICE : ALL MODELS — DO NOTFORCE THE AIR HORN ASSEMBLYONTO THE BOWL, BUT RATHER LIGHT-LY LOWER IN PLACE. IF AIR HORNDOES NOT SEAT EASILY, CHECK ALIGN -MENT OF AUXILIARY METERING RODHANGER (IF USED) .

3. Install air horn to float bowl attaching screws .(Early models have (9), late models have (13), see Figure70) . The (2) long screws go through the secondary side ofthe air horn at rear and (2) countersunk screws go insideprimary bores next to venturi . Install air valve lockoutguard (if used) under intermediate length screw (#4 inFigure 70) and secure with self-tapping screw. If used ,install air horn baffle (secondary side) beneath #3 and#4 air horn screws . Air horn screws (except counter-sunk screws) may or may not use lockwashers dependen tupon application. Tighten all screws evenly and securely(see Figure 70 for proper tightening sequence) .

NOTICE : Do not install air horn screw #5on M4MC-M4ME models using a bowl ventvalve until completion of bowl vent valv eadjustment . Then, install bowl vent valvespring, gasket, and cover, retaining with # 5air horn screw. On 4MV models using th evacuum operated vent switch valve, do notinstall #5 air horn screw until valve cover isinstalled (see Step 7, Page 41) .

4. On 4MC-M4MC-M4ME models, install fron tvacuum diaphragm rod into the slot in lever on the en dof the air valve shaft . Then, install other end of ro dinto hole in the front vacuum break diaphragm plunger .Install front vacuum break diaphragm and bracket as-sembly to float bowl (4MC) or air horn (M4MC-M4ME )and retain with two screws . Tighten screws securely.

'41

9D.5March 1981

Page 4 1

Figure 70 Air Horn Screw Tightening Sequenc e

NOTICE: Do not attach vacuum break hoseuntil vacuum break adjustment is completed .

5. 4MV Models - Connect choke rod into lower chok elever inside bowl cavity. Then install upper end of rodinto upper choke lever and retain rod in upper leve rwith clip .

On other models using the "clipless" rod design ,connect choke rod into choke lever inside bowl cavity ;then install upper end of rod into upper choke lever .Install upper choke lever on end of choke shaft ,aligning slots in lever with slots on end of shaft, an dinstall attaching screw. Tighten screw securely. If an airvalve lockout lever is used, make sure tang on uppe rchoke lever is located beneath tang on air valve lock -out lever before tightening screw.

NOTICE : Make sure that the flats on the endof the choke shaft align with the slot in thechoke lever .

6. If used, install idle vent valve on locating pins afte rengaging with actuating wire . Install attaching scre wand tighten securely .

NOTICE: Some models use a thermostaticallycontrolled idle vent valve . On these, installthe thermostatic bi-metal strip first, the nthe spring arm on top to the bi-metal strip .Then install attaching screw . Install dustcover under air horn screw.

7. On models using a vacuum operated vent switchvalve, carefully install diaphragm and stem in diaphrag mretainer; then install diaphragm and retainer in air horn,

making sure diaphragm is not wrinkled or torn . Lightlytap diaphragm retainer into air horn assembly until fullyseated . Install diaphragm spring over diaphragm ste mand, with stem raised, compress spring while slidingvent valve assembly under slot in diaphragm stem .

NOTICE : Part number and "RP" on ventvalve face upward . Install vent valve covergasket, cover, and screw . Align cover withholes in air horn and tighten screw securely .Install longer air horn screw in vent valv ecover and air horn and tighten screw securely .Install pump override lever on diaphragmstem and retain with small screw . Tightenscrew securely .

8. Install (2) secondary metering rods into the secon-dary metering rod holder (upper ends of rods pointtoward each other) . Install secondary metering rod holder(with rods positioned in secondary metering discs) ontoair valve cam follower . Install retaining screw and tightensecurely . Work air valves up and down several timesto make sure they are free in all positions .

9. Connect upper end of pump rod to pump lever . Iftwo hole pump lever is used, make sure pump rod is inspecified hole in lever, noted at disassembly (or se especifications) . Place pump lever on air horn casting —aligning hole in pump lever with hole in horn casting .Using screwdriver, push pump lever roll pin back throug hcasting until end of pin is flush with casting bosses i nair horn (Figure 71).

Figure 71 Installing Pump Leve r

NOTICE : Use care installing the small rol lpin to prevent damage to pump lever castingbosses .

NOTICE : If the "clipless" pump rod design

9D•5

March 198 1

Page 42F'

Delco

is not used, install pump rod in pump leve rand retain with clip .NOTICE: The front vacuum break, rea rvacuum break (if used), and fast idle ca m(choke rod) adjustments must be performed ,and the thermostatic coil lever inside th echoke housing has be be indexed properlybefore installing the choke thermostatic coi land cover assembly, and gasket (if used) .Refer to the adjustment procedures and speci-fications contained in Section "D" of theDelco Carburetor Parts and Service Manual(9X) .

10. After the vacuum break(s), fast idle cam, an dinside thermostatic coil lever are adjusted, install fron tand rear (if used) vacuum break hoses . Then, thethermostatic coil and cover assembly, and gasket (ifused), should be installed and the cover assembl yrotated until the choke valve just closes . At this point,the index cover should be adjusted . Install three chokecover retainers, and screws where used, and tighte nsecurely .

On late model carburetors where tamper resistantrivets and retainers were removed during disassembly ,(and after the inside coil lever, fast idle cam, chok erod, and front and rear vacuum break adjustmentshave been checked), install the cover and coil assemblyin choke housing by following the instructions supplie din new choke cover retaining kit .

NOTICE: On M4ME models, ground contactfor the electric choke is provided by a metalplate located at the rear of the choke assem-bly. DO NOT INSTALL A CHOKE COVE RGASKET BETWEEN THE ELECTRI CCHOKE ASSEMBLY AND THE CHOKEHOUSING .

11. If the C.E.C. valve or idle stop solenoid wasremoved from the bracket for replacement purposes ,install solenoid in bracket, lockwasher, and retainingnut. Tighten nut securely, making sure lockwasher tab salign with slots in bracket and flats on hex portion o fsolenoid nut . Then, bend back tabs to retain the nut .

If mounting bracket was removed from the air horn

for replacement purposes, install solenoid and bracketassembly on locating lugs on air horn . Then, installscrew securing solenoid bracket to float bowl . Tightenscrew securely . Then crimp bracket tabs on air horn .Install vacuum hose from tube on float bowl to C .E.C .valve .

12. On other models, install (2) screws in bracket toretain the idle speed solenoid, A/C idle speed solenoid ,throttle closing dashpot, or throttle lever actuator to thefloat bowl . Tighten screws securely.

NOTICE: Whenever a service replacementthrottle body is installed on 4MV-4M Cmodels equipped for exhaust emission control(except 4MV Pontiac), the following adjust-ment procedures must be performed carefully :

a. With carburetor assembled, place a .300" plu ggauge or drill in forward vent tube in air horn . Withslight downward pressure on plug gauge or drill, seatpower piston .

b. Using screwdriver, back APT screw in throttlebody OUT until power piston is completely seated .

c. From this position, turn APT screw inward unti lpower piston starts to move upward .

d. From this point, turn APT screw in the speci-fied number of turns listed on the instruction sheetincluded in the service replacement throttle body pack-age.

e. After adjustment, remove plug gauge or dril lfrom air horn and install welch plug (furnished withthrottle body) over APT screw .

ADJUSTMENT PROCEDURES AN DSPECIFICATION S

Refer to the Delco Carburetor 9X Manual "C" Sectionfor Replacement Parts and "D" Section for TroubleShooting, Adjustment Procedures and Specifications ,for each carburetor model . The adjustments should beperformed in sequence listed as applicable to eachcarburetor model .

The 9X Manual, Carburetor Tools and Gages, ar eavailable through AC-Delco suppliers .

9D- 5March 198 1

Page 4 3

TYPICAL EXPLODED VIEW — QUADRAJET PARTS

10

Air Horn Parts1

Air Horn Assembly2

Gasket-Air Horn to FI B3

Lever-Pump Actuating4

Roll Pin-Pump Lever Hinge5

Screw-Air Horn to T/B (Long)6

Screw-Air Horn to F/B (Short )0

Screw-Air Horn to F/B Countersunk )8

Metering Rod-Secondary9

Holder and Screw-Secondary Metering Rod10

Baffle-Air Hor n11

Seal-Pump Stem12

Retainer-Pump Stem SealChoke Part s

13

Vacuum Break Cont & Brkt Asm (Prim )

6

7

14

Screw-Vacuum Break Attachin g15

Hose-Vacuum Break16

Link-Air Valve

8 16A

Link-Air Valve (Truck)10

Lever-Choke (Upper)4 18

Screw-Choke Lever Atch19

Link-Choke20

Lever-Inter Choke Shaft (lower )21

Seal-Inter Choke Shaft (Hot Air Choke)22

Lever-Secondary Throttle Lockout

1023

Link-Rear Vacuum Break24

Inter Choke Shaft & Lever Mm25

Cam-Fast Idl e51

12 26

Seal-Choke Hag to F/B (Hot Air Choke)202

/ 20

Choke Housing Asm .14 50 28

Screw-Choke Housing to FIB

tch29

Seal-Inter Choke Shaft (Hot Air Choke)1549

53 30

Lever-Choke Coi l01 31

Screw-Choke Coil Lever36 48 54 32

Gasket-Stet Cover (Hot Air Choke )55 00 33

Choke Cover & Coil Asm (Hot Air Choke )

4341

34

Choke Cover &Coil Asm (Electric Choke)68 35

Kit-Stat Cover Attachin g599I I 19 42

52 `` 69 36

Rear Vacuum Break Cont & Brkt Asm/Secd5 8

16A

233

5 6P.'\I `9 1

40

66

/.//~/

~~``

_

J J J`~

30

FloatScrew-Vacuum Break Cont Attaching

Yawl Parts38

Float Bowl Assembl y39

Primary Metering Jet As m`

i.) [

38

i y

03 40

Ball-Pump Discharge20

IIII I .L I►o

i

II

_•

41

Retainer-Pump Discharge Bal l

28 25lbs .'.:

~l- 42

Baffle-Pump Wel l43

Needle &Seat Assembl y44

Float & Lever Assembl y

-;; ~—!

h~4'V_

w--t-'

*~ 6 52 9

33

a

ii

t

1 63 45

Hinge Pin-Float Assembly46

Power Piston Assembl y~~1, ~y 40

Spring-Power Pisto n'

6 022

r 6248

Rod-Primary Meterin gY6

21 49

Spring-Metering Rod Retaine r,pa \

31

30

20

24 08

61

60 50 Ei p Return35

04

;• 53

Pump Plunger Assembly80

~i

±—

'--- 54

Link-Pump Plunger55

Baffle-Secondary Bores34 56

Idle Compensator Assembly

1, - C&v

/50

Seal-Idle Compensator58

Cover-Idle Compensator59

Screw-ldle Compensator Cover-

°60

Filter r Nut-Fuel InletELECTRIC

81 61

Gasket-Filter Nu tCHOKE MODELS

09 62

Filter-Filter Inle t08

06 63

Spring-Fuel Filter00 64

Screw-Throttle Sto p65

Spring-Throttle Stop Screw66

Idle Solenoid & Bracket Assembl y60

Idle Load Compensator & Bracket Assembl y68

Bracket-Throttle Return Sprin g69

Actuator-Throttle Lever (Truck Only )00

Bracket-Throttle Lever Actuator (Truck Only )01

Washer-Actuator Nut (Truck Only)02

Nut-Actuator Attaching (Truck Only )03

Screw-Bracket AttachingThrottle Body Parts

04

Throttle Body Assembly05

Gasket-Throttle Body to F/B06

Screw-Throttle Body to F/ B00

Idle Needle & Spring Assembl y08

Screw-Fast Idle Adjusting09

Spring-Fast Idle Scre w80

Tee-Vacuum Hose81

Gasket-Insulator Flange

Figure 72 Typical Quadrajet Assembly

u0t Carbureto rModels 4MV-4MC-M4ME-M4M CService Manual

GM

Delco

Delco CarburetorMODEL 4MC GUADRAJE T

1973-76 GMC MOTOR HOM E455 CUBIC INCH OLDS ENGIN E

PARTS SHOWN ARE FOR IDENTIFICATION ONLY . CONSULT PARTS LIST FOR CORRECT PART NAME AND NUMBE R

eZ-'AID14

15l'M.TIi~~0 _0n

g II 12 13 16vr~U/ 6

7 ®19

~~~_ 17 IN o 2~-22

3 10 208

~9* ~~ro•~ 25

21

27.0

3~230

24 _- ,22 2 92l

AIR HORN PARTS-

CHOKE PARTS

59. 4 158 40 es 66=t. 69~ltlr~ 6 71%

7N56 cam ,

453g'J

37165

33

34.3164

r ~~► _

~ ~ p5 3A 36

43 67`~ ~

6 1

52 50

57

c5tf)*PI) 0

~2" '9 72

FLOATi

BOWL PARTS 55 54, 60 THROTTLE BODY PART S

PARTS IN ALL COLUMNS SAME — EXCEPT WHERE INDICATED

1975-7 61973-74 FED CALIF . APPLICATIO N7043254 7045254 7045554 CARBURETOR No .24-404 24-405 24-406 REPLACEMENT PACKAGE No .

7046812 17051886 17051886 OVERHAUL KIT9258 9269 9269 POWER CARBURETOR KIT

40-419 40-428 40-428 GASKET SE TIllus . No .

AIR HORN PART S1 7047976 7047976 17051386 Air Horn Assembl y2 7029087 Gasket—Air Horn3 7048169 Lever-Pump Actuatin g4 9428787 Roll Pin—Pump & Lockout Lever Hing e5 7029912 Screw—Air Hor n6 7014699 Screw—Air Hor n7 7031105 Screw—Air Hor n8 7045780 Metering Rod—Secondary9 7034522 Sec . Metering Rod Holder Kit10 7037968 Lever—Air Valve Lockou t— 7035344

_Air Valve Spring & Cam Kit

— 7030753 Air Valve Stop

F'

Delco

BULLETIN: 9C-4000DATE: NOVEMBER, 197 5PAGE : 1REPLACES 9C-400 0DATED JANUARY 197 5

CO, WD, 131, 1J2 :16, 9X, 9FR, 9FD PRINTED IN U .S .A .©1975 GENERAL MOTORS CORP .

BULLETIN : 9C-4000PAGE : 2

l 7043254 I 7045254 I 7045554 I CARBURETOR No .Illus . No.

CHOKE PART S11 7036881 Stat Cover, Coil & Gasket Assy .12 7002760 77050961 1705096 1

---Gasket-Stat Cover

_--

-13 7047499 Vacuum Break Control & Brkt . Assy .14 7040031

.__ _ _.v- .--Vacuum Break Control Assy .

15 7038305 Rod-Vacuum __

____16 7038581

_S^rew--Control Attact in g

17 703519.9__._. . -

Cam-Fast Idle ___18 7026339

- _Hose-Vacuu m

19 7038259 Choke Snatt

~-20 70453555 Choke Valve21 7029866 Screw-Choke Valv e22 7031231 Lever-lnlermediate-Cboke23 7038269 Rod-Choke24 7036880 leHousing Assembl y25 - 7038282 inlet Choke.

ft&!,,ever-

s y.

- 7037569 Sea :~-Inter.

hake S Taft7030662 -.7043367

: .. 3367_

_

• td =owl26 7038285 SEENEWMEEMEMOME27 r

r : 5ltrex~r- Goi

y r28 r

r : =111111MIE .,

<ChokeHs•toBowl --

-2930

7n387029866 ErinMM. Screw-Choke Lever

31 7000614, - etain r-Stat Cover

-32 7011271 ~~„ crew-Stet Cover

LOA BOWL PART S33

•7046757

'•

Rt~'•wl Asset--34 7031970 r c

' n r je

imar35 7002117 z Ball-Putn Disx arse

-

36 - -7029849 ' -; Retainer

umpDisehar eBal l37 _ ~__- 142-30

--edle & SeatAss

38 _~ KI T JNLY

r1 :_ ~iy' /Lea ke .

=die Seat

-39_ 7033731 I'

Ul [oat Needle40 ?03;T~ oat Arse b I41 7'029856 -nge Pi

Float Assembl y42 7034903

_,Power Piston Assembl y

43 7036019 ._

.

• wet Piston44 7046338 :. :' ` od-Primar45 7029862 • rin•,.

eterin • ; °

•-=Primar

-46 7^45878 _.

ter Nut-Fuel Inlet47 7024281 asket-Filter Nu t48 ~r

t1 1_ _

49 !

7032'Q o.s __ _5'0_ _

51IdleCompensator Assembly

slie t̀-Idte Cofinpensato r52 - _,,,,

3v r--0le Co.rp ensator53 - :"i . .

i- .

a Scre

. ~- Art : hin•

-

54 7003176

. .rin •

• . St . • Screw55 700212 E rew=ldl-S

o ~

56 7034361 }~

d{M® insert-Fleet - w l57 703136b :Baffle-Float'llowl58 7004 ^T_ : '. rtr~, .

704 ''h~6•

. . ?.` 7041169 . r n-

-urn . Retur n59 7035Q31_ M EE" um • Assembt60 7026138 .

w ., .

. THROTTLE BODY PARTS61 7046811 17052803 17051396 Throttle Body Assembly62 KIT ONLY Gasket-Throttle Bod y63 7035790 Screw-Throttle Bod y64 7048532 Idle Needl e65 7011479 Spring-Idle Needl e66 7038298 Lever-Cam Followe r67 7035772 Spring-Cam Leve r68 7035998 Fast Idle Leve r69 7035523 Screw-Fast Idle Lever70 7044794 Screw-Fast Idle Adjustin g71 7029900 Spring-Fast Idle Screw72 412501 419047 419047 Gasket-Flange

nDelco

Delco Carburetor

MODEL M4MC QUADRAJET

1977 GMC MOTOR HOM E403 CUBIC INCH OLDS ENGINE

BULLETIN : 9C-400 1DATE : NOVEMBER 1977PAGE : 1REPLACES 9C-400 1DATED NOVEMBER 197 6

PARTS SHOWN ARE FOR IDENTIFICATION ONLY . CONSULT PARTS LIST FOR CORRECT PART NAME AND NUMBE R

0''', !11111PL,iboo.~

—

•ti

T1

J11

12

14

=.-'a13

15

S1;o}( .17

l8 p

S3'

23-20 .,. .~~ a4

•

1

O

21

AIR HORN PARTS"` CHOKE-PARTS

30

32

29i

s _

5

'O--us+n E

11

'3,1

} S r

6 7_

V e

?i--

rm„,t _, 37,o, 6. . cam.

®~

<

.

_ 3aT_~►

~-a ,h ~Q~~`

5311 ;TAU} a 61 ~

~

52

4 . .~ .

-far, .

~ I l ' °”' i4

1111)

' 48

49 M

}_ .

FLOAT BOWL PARTS

Ifi

`~ 4 1 . , 3 THROTTLE BODY PARTS

PARTS IN ALL COLUMNS SAME — EXCEPT WHERE INDICATE D

FE0 A _-w _ CALIFORNIA APPLICATIO N17057154'- :̀~ :J -- -

-17057.559

k ;. : -CARB U RETIR RJllo _'-REPLACEMENT

No .170 17055023 -OVERHAUL . FT

A .9319 4319:7-

._NER CAR UR

R KI Tao-asa __ 40-454 GASKET SET-- ,

rt.Illus . No .

71" :

e , N;PARTS1 17055497 17055'919

+ r: Ff''Pit1-Horn Assembl y

2 .17051797 Gaskiet-Air Horn3 7048169 Lever-Pump Actuating4 9428787 Roll Pin—Pump & Lockout Lever Hinge5 7029912 Screw—Air Hor n6 7014699 Screw—Air Hor n7 7031105 Screw—Air Hor n8 7045780 Metering Rod—Secondary9 7034522 Sec . Metering Rod Holder Ki t

10 — — Lever—Air Valve Lockou t— 7035344 Air Valve Spring & Cam Ki t— — — Air Valve Stop

CO, WD, 131, 132 :M, 9X, 9FD PRINTED IN U .S.A.© 1977 GENERAL MOTORS CORP .

BULLETIN: 9C400 1PAGE : 2

11 17054309 Stat Cover, Coil & Gasket Assy .12 17050961 Gasket-Stat Cover , -.13 7044435 Vacuum Break Control & Bracket Alp .14 :,•, ; .

,. Vacu,l m iireaic Control Assy .15 7041527 Rod-Vacuum16 17050732 Screw-Control Attachin g17 17Q566 91 17056632 Cam-Fast Idl e18 7

339 Hose-Vacuum19 7038259 Choke Shaft20 704890.4 _ y Choke Valv e21 7029 :6 . Screw-Choke Valve22 7031231 Lever-I ntermediat -e`Chbke23 70411 ;472 Rod-;Choke24 17055095 Choke Sousing Assembl y25 _ 7041492 -1nterme late-Gh . ,- Shaft & Waver Ass- r7O375 .

==:r

. -Seal-1

'mediate

ho eS af t'70 4

3 . .

. .._ - Seal=

. _,26 704336: ,Z- sl:̀27 0

o ° 'crew--- •il

-ever

S28 -Screw ahdke Hs. . to Bowl -'

pro : .

r. -29 70 . ..3 0 — • :6 rew-Choke Leve r31 .00614 Ret-iner

tat Cove r32 ;=~

701- 270

? . . . . ~• '

Scr

-S at Cover - ,,,.

= LPARTS1:70554 . 8 "

'1705592V Flo : B•'`°` Assembl—

34 7031975

: <, o

'i ' Jet

r i7 0 ®2117 Ball-Pum • Disch

- -

36 •- ~9

- ; etainer-P '

• iiischar .e Boo.

.; .. .Nee .. & Seat Ass . ._ 38 a

`. x Gasket-N

die Sea t- -'9 ` "oat Needl e

M2 ~~. "

loot . ssemb l—

41 Hinge•Pin-Float Assembl y_•

42 0 "

• Power Piston Assernbl43 -taw St.

5• b otraet Pisto n44 o

955 , -~~-

.Ro'd=-Prima r_

45 o- r

$Frog-

ele:ring Ro•rimary--. ;—

46 Nut-Fuel Inle t_

47 :. . asket-Filter Nut

- .

t

. ,4& . -. i

_le ,

495051

NiFniff'"' sa Qv:_ ea

= d ° C .

Att52.

i

'o`rov

ldle-Com

n ator53 -.

rew-Cover Attadlilnlgk54 0 0 Sprin -Idle Stti S($

nt55 o . -

crew-Idle

tay

--_,

,56 70' 14, .1' = inser

oat-Bowl57 :703 :158_

--_ - .'

s' prr

um p. Retur n59 170530721 - =

=. ifigarnalOUMMIM Pum• Assembly

'60 7026138 -- ,

._ott ' 13

- 70, .

0

:_; . . ( UNIMMUMMMEEM) Insert-Aneroid

vi t- 7041473' x: ,

:' Lever-Secondary Lockou tTHROTTLE ~Bfll'3Y PARTS

61_L1_170.8_885' 1 57054744 Throttle Body Assethb̀ly62 KIT ONLY Gasket-Throttle Bod y63 7035790 Screw-Throttle Bod y64 7048532 Idle Needl e65 7011479 Spring-Idle Needl e66 7041497 Lever-Cam Followe r67 17051494 Spring-Cam Leve r68

-7041498 Fast Idle Lever

69 7036079_

Screw-Fast Idle Leve r70 7044794 Screw-Fast Idle Adjustin g71 7029900 Spring-Fast Idle Scre w72 419047 Gasket-Flange

17057254

i

17057559

CARBURETOR No .Illus . No .

CHOKE PAR T

I

De1co Carburetor

MODEL M4MC QUADRAJET

1978 GMC MOTOR HOM E403 CUBIC INCH OLDS ENGIN E

PARTSSHOWN ARE FORIDENTIFICATIONONLYcCONSULT PARTS LIST FORCORRECT'PAR*AME AND NUMBE R

.-rA.

Ir-;is,

5l~ V.- ;orl

._II

_--

''02=11219

14

1516

r";

'

. 22

239i'f'

-

"_ 19J

)'

f OH

0 .13 ,86 f)4=9

- 044: 'r

00 ,'s- erO VAIR ...HORN_MRTS 4#44)f(E#Afitt.s 6(:t_,t g.qL_ , R_.

_

j 419VI) 9R . rAl

.

-113 '1„„--

,Mlp*^1110 r f :• a c ^1-

JQ

0110 '804

--.--- B8-07

4111&\

4-7-19AIS1 9

'' = 9

"- 47-

cz),,, oft 1I.,,.

,

i---i'q

tit-i

-

D 9

n.1,f)

R4, +

. . ;

49

FLOAT IIOVIL FnAt4tt _20! 127 1, 12!

PARTS IN ALL COLUMNS SAME —EXCEPT WHERE INDICATE D

_ . MMOMiralhn '' 1511559._ _

rt._J1St

&E-Noi

..____. __=,. =I= MAUL-

-- --

_ ___=11111111111F.' 'W.CTIETT,t-' KIT-

--t- '

--MijiMMIMMM . 3'coF.ao ,

Iles .

o .

At. . . . ''WIM11111111111MMI1111111EMEE.11IN ao

AM1081MISPH1111*1111IMMIll Vilf1lixvUer MrO . • ir

cittkr

..

. ,7048169 a, sit .'

evor F-ParIvIsictntati4 9428787 ybo i Roll Pin-PumWkUtII(lout Levet Hinge

, a5 7029912 t

. ._

Screwi-Air HotnIf,C16 7014699 Screw-Air Hofri7 7031105 Screw-Air Horn

--

8 7045780 Metering Rod-Seconda r9 7034522 Sec . Metering Rod Holder Ki t10 Lever-Air Valve Lockou t

7035344 Air Valve Spring & Cam Ki tAir Valve Stop

BULLETIN : 9C-400 2DATE : NOVEMBER 1977PAGE : 1

CO, WD, 131, 132 :M, 9X, 9FD PRINTED IN U .S.A.© 1977 GENERAL MOTORS CORP .

BULLETIN : 9C4002PAGE : 2

Illus . No .17058254 I 17058559

CHOKE PARTSCARBURETOR No .

11 17054309 Stat Cover, Coil & Gasket Assy .12 17050961 Gasket—Stat Cove r13 7044435 Vacuum Break Control & Bracket Assy .14 — — Vacuum Break Control Assy .15 7041527 Rod-Vacuu m16 17050732 Screw—Control Attaching17 17056631 17056632 Cam—Fast Idle18 7026339 Hose—Vacuu m19 7038259 Choke Shaft20 7048904 Choke Valve21 7029866 Screw—Choke Valve22 7031231 Lever—Intermediate Choke23 7041472 Rod—Choke24 17055613 17065040

_Choke Housing Assembl y

25 17050754 Intermediate Choke Shaft & Lever Assy .— 7037569 Seal—Intermediate Choke Shaft— 7043367 Seal—Choke Hsg . to Bowl26

_7043368 Lever—Stat Coi l

27 7019709 Screw—Coil Lever28 7038808 Screw—Choke Hsg . to Bowl29 7041542 Lever—Chok e30 7029866 Screw—Choke Leve r31 7000614 Retainer—Stat Cove r32 7011270 Screw—Stat Cove r

FLOAT 3OWL PARTS33 17055633 17065039 Float Bowl Assembl y34 7031974 7031978 Jet—Primary35 7002117

_Ball—Pump Discharge

36 7029849 Retainer—Pump Discharge Bal l37 30-134 Needle & Seat Assy .38 KIT ONLY Gasket—Needle Sea t39 7033751 Pull Clip—Float Needl e40 7046300 Float Assembl y41 7041469 Hinge PinFloat Assembl y42 7044449 Power Piston Assembl y43 7036019 17055329 Spring—Power Pisto n44 17056953 17051353 Metering Rod—Primary45 7041459 Spring-Metering Rod—Primary46 17059861

_Filter Nut—Fuel Inlet

47 7024281 Gasket—Filter Nut48 GF-441 Filter—Fuel Inlet49 7032732 Spring Fuel Filter50 — Idle Compensator Assembly51 — Gasket—Idle Compensator52 — Cover—Idle Compensator53 — Screw—Cover Attachin g54 7003176 Spring—Idle Stop Scre w55 7002121 Screw—Idle Stop56 7041471 Insert—Float Bow l57 7031365 Baffle-Float Bow l58 7042979 Spring—Pump Return59 17053072 Pump Assembl y60 7026138 Rod—Pum p— 17051796 Insert—Aneroid Cavit y— 7041473 Lever—Secondary Lockou t

THROTTLE BODY PART S61 17058648 17058984 Throttle Body Assembly62 KIT ONLY Gasket—Throttle Bod y63 7035790

_Screw—Throttle Body

64 7048532 Idle Needl e65 7011479 Spring—Idle Needl e66 7041497 Lever—Cam Followe r67 17051494 Spring—Cam Leve r68 7041498 Fast Idle Lever69 7036079 Screw—Fast Idle Lever70 7044794 Screw—Fast Idle Adjustin g71 7029900 Spring—Fast Idle Scre w72 419047 Gasket—Flange