Rejetting the CV Carburetor

contributed by L. Maurice Riggins (1998)updated by L. Maurice Riggins (2001)updated by L. Maurice Riggins (2005)

IntroductionThe author strongly encourages you to stay out of the top of the carb. The slide diaphragm can be extremely difficult to reinstall without splitting or pinching the rubber. But the main reason is that there is seldom a reason to go into it, and there are several reasons not to.

The slide vent hole is the size it is for a reason. Like a shock absorber, it damps the movement of the slide. If it is drilled to 1/8" as is commonly done, the slide will open too fast when the throttle is whacked open suddenly and it will overshoot where it should be, then as a result, fall back down, but do it too fast, overshooting where it should be again. This results in oscillation, and a huge variance in mixture. The diaphragm spring establishes the constant velocity. Changing to a lighter spring, or worse yet, cutting coils off the spring, lowers the constant velocity, and this is the velocity that creates the vacuum that sucks fuel up from the fuel bowl. Even if you increase the jet sizes to compensate, the mixing becomes erratic. You can see evidence of a drilled slide or lighter spring as a dip in the torque curve just after the throttle is opened. Blindly shimming the needle up or replacing it is not recommended. Late model needles are richer, sometimes more so than aftermarket. The only time this is required is when dyno tuning. In the process of dynoing, starting with a small main jet and doing runs with progressively larger main jets, if going up one main jet size causes high rpm horsepower to fall off (i.e. if you've just gone past the optimum main jet size) but low rpm power improved, go back to the previous main jet size, and shim the needle up .030" or so with a small washers. This is not common, and seldom required. And finally, although it may result in less than optimum idle mixture, you CAN temporarily skip the part about drilling the plug off the idle mixture and setting the idle, if you are concerned about warranty issues. By increasing the size of the slow jet, you are automatically making the idle mixture richer, and the factory setting is often pretty close. Idle performance is usually adequate. The sign that it isn't is an occasional stumble when the throttle is applied at idle. The author encourages you to "do it right" and perform this step if possible.

RejettingAfter removing the old air cleaner per the instructions, but before installing the new high-performance unit:

1. Turn the fuel valve off. 2. Find the fuel bowl drain hose end (front of the engine behind the oil filter and put

it in something (non-glass) to catch the gasoline. 3. Looking at the backside of the carb between the cylinders from the left side of the

bike, find the fuel bowl drain screw on the bowl and using a long skinny

screwdriver open it counterclockwise about 3 turns which will let the fuel bowl drain, then close it back.

4. Using an 11/16" open end wrench, loosen the nut on the backside of the choke knob bracket and slide the choke knob/cable assembly out of the slot in the bracket. Don't rotate the plastic nut on the front... it adjusts the tension on the choke ("enrichener") cable.

5. You'll have to use an awl, skinny screwdriver, and perhaps needlenose pliers to remove the one-time-use hose clamp on the gas hose at the tank, destroying the clamp in the process, so have a replacement worm-drive hose clamp from the hardware store for later reassembly. Slide the hose off the tube on the fuel valve. You may have to grab the hose with pliers and rotate it back and forth to break it loose, but don't let the plier's teeth cut into the hose. Do not remove the vacuum hose (behind the fuel hose) from the fuel valve.

6. Back on the right side of the bike, find the vacuum hose that plugs into the top of the carb behind the black plastic cap and pull up on it until it slips off the tube coming out of the carb. Note here now the routing of the fuel hose going to the tank and the choke cable so you'll get them back in the right places during reinstall.

7. Find the fuel bowl drain hose and fish it out from behind the front cylinder pushrod tubes and behind the oil filter so it's loose.

8. Put a big thick towel on the crossover exhaust pipe and engine case below it to protect them from getting scratched by the carb or tools. (actually it's better to do this before you start pulling the old air cleaner off).

9. With one hand on the top of the carb and one on the bottom start rocking the carb in at the top and out at the bottom, then do the reverse, back and forth, all while pulling the whole thing toward you. Don't let the carb rotate side to side or it may scratch the rocker covers. The carb will POP out of the rubber gasket on the manifold with the throttle cables still attached to it, and it will be pulling the fuel hose and choke cable through the mess between the cylinders.

10.You can lay the carb hanging from the throttle cables on the towel if you need to grab tools, or use both hands for other things.

11.Rotate the carb up so you're looking at the bottom. On the back, behind the fuel bowl, you'll see what looks like about 1/4" silver plug. This covers the idle mixture adjustment screw and we are going to drill a hole in it, screw a sheet metal screw into that hole just until it bites good, then grab the screw with a pair of pliers and pull it and the plug out.

12.Prepare an 1/8" drill bit by using either a drill stop or several turns of electrical tape around the bit so that it can't drill into the plug any deeper than about 1/8". If it does, it may break through too hard and plunge into the screw. If that happens the screw may be gouged up a little, but even worse, it may spin closed (clockwise) hard, damaging the idle mixture needle and seat. So don't put a lot of pressure on the drill, use a sharp bit and let it do the work. Drill the hole in the center now.

13.Start a self-tapping sheet metal screw into the hole until it bites good (it may even start spinning the plug), grab it with a pair of pliers and pull the screw and plug out. You should see the idle MIXTURE screw.

14.Before removing the fuel bowl, note how there is a rod coming down from the throttle linkage into a bellows on the bowl. You'll have to put this rod back in the bellows when reinstalling the bowl. Also, note in the mouth of the carb there is a brass pipe standing up in it. This is attached to the bowl and slides up through the carb body during bowl reinstallation.

15.Find the four brass screws that hold the bowl on the carb. Using a phillips screwdriver that completely fills the slots in the screws remove them without letting the screwdriver slip and damage the screws. This may take considerable pressure. When removing the screws, hold the bowl in position until they are all out then pull the bowl off straight down. Be extremely careful... the floats are just inside the bowl. The rod will come out of the bellows and hit against the carb body... no you didn't drop it. Set the bowl (with dangling drain hose) aside some place clean. Note the brass tube on it that was sticking up in the carb mouth.

16.You will see the floats hanging from the bottom of the carb. Be extremely careful not to push on these in ANY direction. The metal holding them is thin and will bend easily, getting the floats out of adjustment. Also, if you push up on the floats hard, you may damage the needle and seat they control. If you lay the carb down on the towel make VERY sure the floats aren't touching anything.

17.Looking at the bottom of the carb, find the two jets. The main jet will be more or less in the middle, screwed into the emulsion tube and should say "160" on it for an 883, "170" on it for a 1200, or 190 on it for a Sport or International model. The emulsion tube will have flats on it for a 5/16" wrench. Hold the emulsion tube from turning with the wrench and using a common (flat) blade screwdriver that's wide enough to fill the slots on both sides of the main jet, unscrew the jet (counterclockwise).

18.Screw in the replacement main jet as follows: SE air cleaner OR SE mufflers BOTH 883 #165 #170 1200 #175 #180 1200 Sport/Intn'l #195 #200

Tighten firmly, but do not strip. Do not use LockTite.

Note: These jet sizes are a good place to start, but realize that some tuning may still be needed. Some 1200's come stock with larger jet sizes and altitude can play a big role in jetting... if you live above 3,000' above sea level, you may not need to rejet! And if you live right down at sea level, you may need to go larger. Also, I have heard that CA bikes come from the factory with larger jets due to emissions equipment on the bike. The ONLY accurate way to get the main jet set correctly is on a dyno... PERIOD.

WARNING! The above jet recommendations are for '03-earlier rigid engine Sportsters. It has come to the author's attention that Harley is jetting '04-later rubber-mount Sportsters even richer than these recommendations, which themselves tend to be slightly on the rich side. Some recommend not changing their main jet size, while others even recommend reducing it. Since I don't know

what changes were made to other parts of the carburetor, and have no experience with these models, I'll refrain from making a recommendation.

19.Find the slow jet on the carb bottom. It should say "42" on it and you'll replace it with a #45. It will be down in a tube cast into the carb body. You must find a screwdriver with a blade wide enough to fill the slots in the jet that doesn't taper wider above its tip, or it won't fit down into the tube to reach the jet. You may have to have a machine shop grind a screwdriver down so that it's shaft is no wider than the blade at the tip. Do not try to force an inappropriate screwdriver in or you will crack the cast carb body. Unscrew (counterclockwise) the #42 slow jet and replace it with a #45 slow jet. Tighten firmly, but do not strip. Do not use LockTite.

Note: The #45 slow jet is the stock slow jet in Twin Cam 88 engines. As with the XL, the stock slow jet is replaced with one size larger, so the dealer's service area, or a buddy with a Big Twin, may have this jet laying around, and you might be able to get it for free.

20.Reinstall the fuel bowl on the bottom of the carb, taking care to: 1. Line up the brass tube that goes up into the carb mouth. 2. Get the rod from the accelerator pump into the bellows, and 3. BE CAREFUL NOT TO CATCH OR BEND THE FLOATS.

21.Reinstall the four screws holding the bowl on the carb bottom. Do not overtighten. Do not use LockTite.

22.Check the rubber seal on the manifold to make sure it is seated on it all the way around.

23.Push the carb back onto the manifold making sure the fuel hose and choke cable are going back where they came from. Rocking helps, but don't worry whether the carb is tilted just right at this time. It will be lined up when you reinstall the breather bolts on the air cleaner (or air cleaner support bracket for non-SE air cleaner).

24.Slip the vacuum hose back on the tube on the top of the carb. 25.Reroute the fuel bowl drain hose back where it came from. 26.Back on the left side of the bike, slip the new hose clamp over the fuel hose and

slide the hose back on the tube from the fuel valve. Slide the clamp up near the valve and tighten, but do not overtighten.

27.Slide the choke knob/cable assembly back on it's slot on the bracket and tighten the nut on the back with fingers, then tighten a bit more with the 11/16" wrench. Do not overtighten or the plastic assembly will crack... just enough to keep it from sliding out of its slot. Pull the choke knob out, making sure it comes out as far as it did before and stays there. If it doesn't come out as far, loosen the nut on the back, check the routing of the cable, then try again. If the knob doesn't stay out, loosen the nut on the back and turn the plastic nut on the front clockwise a little and try again.

Finish installing the new air cleaner per the instructions and remove the old towel..

Setting Idle Mixture and SpeedNote: This MUST be done with the air cleaner installed because it affects the idle mixture significantly.

1. With a flat blade screwdriver, turn the idle MIXTURE screw (the one you drilled the cap off) full in (clockwise) GENTLY until it seats... GENTLY (get the picture?), then turn it out (open, counterclockwise) exactly two full turns. Leave the idle SPEED screw (top right side of the carb looking at it above the air cleaner) where it was before.

2. Turn the fuel valve to on, pull the choke fully out, and start the engine. If you drained the fuel bowl, it will crank for as much as 20-30 seconds without starting while the bowl fills. Once the engine has started push the choke in about 1/2 way and then wait about 2 minutes. Then push the choke in all the way, and if you must do so to keep the engine running, open the throttle slightly. You can keep it there with the throttle lock, the star shaped screw below the right switch housing. Once the engine is fully warm (rear rocker cover is hot to the touch), fully release the throttle lock and make sure the throttle is fully closed. The engine should be idling, perhaps nicely, perhaps not.

3. With a flat blade or phillips screwdriver, turn the idle SPEED screw in (clockwise) about two full turns until the engine is idling fast. WARNING: the crossover pipe is HOT. You should adjust the idle MIXTURE with at least heavy cotton or leather work gloves (not your good ones) to protect from burns. Use a short screwdriver so the handle will not melt on the crossover pipe.

4. With a flat blade screwdriver turn the idle MIXTURE screw in (clockwise) GENTLY until it fully seats. The engine should not die. If it does, turn the idle MIXTURE screw back out the two full turns and go back to step 3, increasing the idle speed setting (in clockwise another turn).

5. Now turn the idle SPEED screw out (counterclockwise) just until the engine dies or is stumbling badly. The idle speed is now set correctly. This is an easy way to set it without a tach. It will result in the idle speed being a little high, which will give more oil to lubricate the engine. If the idle speed is too low, insufficient oil will be pumped.

6. Now turn the idle MIXTURE screw out (counterclockwise) exactly two full turns out (counterclocwise), restart the engine if it died, and let it idle a minute or so to stabilize.

7. The following takes a good ear for engine speed. As the idle MIXTURE screw is turned in clockwise, the mixture will become lean and the engine speed will start to decrease. As it is turned back out counterclockwise the engine speed will increase and stay there for awhile as you continue turning out, and then the engine speed will starts to drop as the mixture gets too rich. Note the points where the engine speed started to drop and set the idle MIXTURE screw in the middle of that higher speed range. Now the idle mixture is set correctly.

How to (properly) Re-Jet a Carburetor

contributed by Lee C. Bussy (2006)

For many years, the "common wisdom" of going up one to two jet sizes when adding pipes and an intake on the Sportster has been gospel. In order to eliminate carb farts, people recommend going up a size on the low-speed jets. When I bought my first Sportster back in '03 I dutifully followed the advice and was rewarded with fair results. When shortly thereafter I began my quest for more power, I began to apply a more critical set of criteria and examination to this methodology.

I had some lengthy discussions with Art Northrup and Dale Amsden about a starting point for tuning my new 1200 conversion, and that's when it hit me: these things are no different than any other internal combustion engine. There's no secret to it, you add gas and air in the correct proportions and they reward you by making noise. Once I began to apply what I already knew from tuning cars and import bikes, the rest was easy. I'll share what I learned, all in one place, so that in the future I don't have to type this in bits and pieces as folks ask questions.

Disclaimer: This works for me. If you did it differently, you probably will feel the need to argue with me. I don't care, I know this works. :-)

Greatly simplified for discussion purposes, there are three ways that the Keihin Constant Velocity 40mm (CV) carburetor meters fuel for us under normal, fully warmed up riding conditions. These are the idle circuit, the midrange metering, and the main circuit. Each of these must be tuned correctly, and in some cases they "overlap" so they must be tuned in the proper order. I will explain the tuning of each circuit and when this must be done.

First up: the idle circuit. This is the one that 95% of the folks I see posting, and talk to in person, don't do right. It's also the one that stands to have the greatest impact on their riding satisfaction. Most people here would be completely happy with the results obtained by just doing this adjustment. One of the biggest complaints about a carbureted Sportster is the "carb farts" or the big stumble that happens right off idle as you start out. There are two areas that can impact this and the idle is one of them. Many dealers, many "experts" recommend going from the stock 42 to a 45 low speed jet. I've even heard of some folks using a 48. This is way wrong in most cases. Yes it works but it's a crutch and is simply not optimal.

"Common wisdom" states that you adjust the idle mixture with the screw: if you cannot make the engine stumble by enrichening the mixture then you need a larger jet. This is only partially true. While it's true that a larger jet will raise the band in which the idle may be adjusted, and it's true that you should split the difference on the idle screw adjustment between lean stumble and rich stumble, most folks set themselves up for a "false failure". What happens is the idle speed screw is set for a proper idle speed (900-1000 RPM) and this means the butterfly is open slightly. A view inside the intake port

side of the carburetor will reveal the idle transfer ports. When the second set is exposed to the intake pulses/vacuum, the idle circuit does not pull as effectively. This is by design, it is supposed to stop adding fuel as the other systems take over.

The solution? When one begins the tuning process, he or she should make sure the bike is warmed up fully. Then the idle mixture screw (IMS) should be adjusted to a good starting point - generally 2.5 turns out from lightly seated is a good place to start. At this point the idle speed should be adjusted as low as possible while still keeping the engine running. No it will not remain here, so we need not be concerned about oil pressure. Ideally the idle speed screw will be backed off fully, allowing the butterfly to close fully. At this point the IMS should be adjusted. It's not necessary to adjust one war or the other till the engine stumbles, only until the idle speed drops noticeably. Move the other direction until the idle speed drops, and then set the screw to the midpoint between those two settings. Raise the idle back to the proper level and your idle mixture is set properly.

Notice I said nothing about replacing a jet. The stock 42 should be plenty to provide the gas an 883 or 1200 needs. At this point, many folks will have a bike that runs well and they will not want to mess with it any further. I say enjoy. If you are still experiencing carb farts, read on.

I'll call this step "Alternate 2A": The Needle. The reason I say "alternate" is this is one path you may choose. If you are not going to be adjusting the white open throttle (WOT) mixture (and most people really don't need to) then this is the next place to go. The needle, it really looks more like a nail, is what slides in and out of the main jet, providing more or less gas as the engine load and speed increases. The needle is tapered and this controls how much surface area of the main jet is exposed for a given position. The needle is part of the slide mechanism and protrudes from the bottom of the slide. It is visible by peering onto the carb throat, it runs right through the middle.As the velocity of air flowing through the carb increases due to engine speed, it creates a low-pressure area under the slide (Bernoulli's principle). This causes the slide to rise up, lifting the needle with it. The CV carb attempts to keep the same velocity going through the carb in this manner, hence the name. In this manner the carb uses the needle and the main jet to control the mixture at anything less than top RPM WOT conditions.

When we get "carb farts" the bike is going extremely lean and the engine misfires. The reason is the butterfly has opened and the velocity, despite the best efforts of the carburetor, has not caught up with the engine and not enough gas is metered. The accelerator pump handles some of this, and some more advanced tuners do tinker with this area, but there is an easier way for us. In 1988 the CV was introduced on the Sportster and this first version had no accelerator pump. To combat the flat spot off idle with no accelerator pump, a needle was used that considerable richens the mixture at this point: its designation is N65C.

We can use the N65C needle, or its close cousins the NOKK or NOKV, to richen the mixture slightly at this point without resorting to larger jet sizes that will likely cause the bike to run too rich everywhere else. A combination of the idle mixture and the needle change has "cured" 90% of the bikes I've worked on. Some folks will tell you that opening the top of the carb is somehow more likely to create issues for you. Well I suppose if you are a hammer and pry bar type this may be the case. I'm going to assume for the sake of this post that you are capable of a reasonable amount of care.If, as happens in some instances, the needle change is not enough to fully cure the stumbles, the next step would be to shim the needle. Simply place a couple of small grass washers, commonly available in a hardware store, under the head of the needle to raise it slightly. For the more anal types, these are approximately 0.020" thick; I shoot for 0.040" of shim for a start.

It is my earnest belief that coming this far is all most people need to do. If you have a big-inch motor, or have a highly modified set of heads or radical cams, the next step may be needed.

The Main Jets: This is step "Alternate 2B". If you do this, this comes first before doing the needle. The reason is the main needs to be sized for peak HP at the maximum RPM the engine will run. You would use either plug shops or some sort of air fuel ratio (AFR) measuring device to set the main jet. The carb is running fully on the main jet ONLY at max airflow through the engine so for the first time through you ignore the AFR at anything but the area near redline.

Once you get the correctly sized main jet, and assuming you first did the idle mixture properly, you then go back to the needle and make the cruise and lower RPM ranges operate at the correct AFR. This is really where the voodoo comes in - there's no reference for carb tuners for the CV's needles. Keihin says it's up to H-D and H-D provides nothing. The good news is the N65C or NOKK, with or without shims, seems to be an excellent all around needle for cruising and for performance.

It's important to remember when looking at a dyno AFR chart that it shows only WOT if that's what you asked for. If you want to see what you are cruising at, ask the dyno operator to check at 70 MPH and 30% load to see where things are. Unless you are a drag racer, this is where you will spend most of your time.

How do you interpret those graphs? There's some experience that comes in here of course. In general, the main jet will move the entire line up or down and the needle will affect the shape of the curve. If you need to "lift up" the left (low RPM) side of the curve then you would shim the needle. Here we can also get into spring rates and the size of the metering orifice on the slide.

This is all pretty advanced stuff and if you get here, I hope you don't rely on printing this and reading it in the garage. You need the assistance of an experienced tuner and this is not really something you can learn reading email on the Internet. Get someone to take you under their wing. Research the subject, read everything you can about theory,

because not only will you be messing with the carb at this point, but the exhaust, advance curve and timing as well. If you do end up asking here or elsewhere for help, having a dyno chart that shows the AFR will be a vital part of someone being able to help you.

I hope this has helped or will help some of you either now or in the future. I have purposefully not gone into how to do the work, I assume that you know how to do it or have one of the other excellent resources available. Good luck, and remember: it's not rocket science.Lee C. Bussy

Read the attached article by Joe Minton, a well respected source of CV and Mikuni carburetor information.

American Thunder Carb Jetting Simplified

Joe Minton Rider Report

Tuesday July 22, 2003 From the August 2003 issue of American Rider

I get a steady flow of questions regarding carb jetting and the Dynojet kits, and I'd like to

answer them once and for all. Before addressing this, I need to set the stage about fuel mileage. The mileage one records is dependent upon a number of factors. The speed at which you travel is one. Mileage plunges dramatically above 60 mph or so-a bike that gets, say, 45 mpg at 60 might only record 30 at 80 mph. Another important influence is the size of the hole you and your bike poke in the air. An FLHT touring rig needs about 12.8 horsepower to go 60 mph, while a Sportster gets along at 60 with about 10. Headwinds, climbing and elevation all affect fuel mileage. Total gross weight has little influence at steady speeds; however, carburetor jetting has dramatic effects on fuel mileage. When I talk with someone about fuel mileage, I find it useful to set a test standard. Here is my standard: a steady 65 mph on a flat, windless road. These are conditions most of us can find and safely use. Using this standard, stock Harleys typically deliver 45 to 55 mpg-the lower for the big touring rigs and the higher for the Sportsters. I have found that properly jetted Evo, Sportster and Twin Cam Harleys deliver mileage between 42 and 51 mpg, using the test standard defined above. Keep in mind that stock engines are tuned very much on the lean side of correct jetting. When we modify carburetors to get rid of the "lean staggers" during warm-up and to smooth out throttle response during acceleration within the lower throttle settings, we can expect somewhat lower fuel mileage at cruising speeds. However, that loss need only be a couple of mpg, not 10.

I have talked with many (easily more than a hundred) owners who have installed the Dynojet kit and who have been disappointed with the results. From your bike's mileage I would guess that you have either a Dyna or Softail series motorcycle; 36 mpg is about

right for a Dynojet- kitted FX Harley. The big touring machines usually get closer to 32 with the Dynojet kit. An FXD or FLST that delivers 36 mpg at 65 mph is running too rich. That too-rich condition has consequences. Range is an obvious possible problem, although some riders aren't too concerned about range as they like to stop more often than the bike needs a fill-up anyway. Climbing ability is a more important concern for those of us who need to go up or over mountains. A 36-mpg bike will probably start misfiring due to its over-rich condition by 4,000 feet, maybe even 3,000. By contrast a stock or correctly jetted engine should get to at least 6,000 feet before getting grossly rich, 7,000 feet is better and achievable. Stock Harley jetting is very lean from just off idle to about 1/4-throttle. This is also true of all road-going bikes sold in America for the last quarter century. However-and this is important-at idle and above 1?4-throttle the jetting is pretty good. Harley's Keihin CV (constant velocity) carburetor is based on the basic Amal slide carb design from the early post-World War I era. And therefore, it shares similar parts which perform similar functions. Idle and just off-idle air/fuel mixtures are controlled by the idle jet which is fine-tuned with a screw. Both the jet size and screw setting are important. Off-idle to approximately 1?4-throttle mixtures are controlled by the straight-diameter part of the needle together with the inside diameter of the needle jet, in which the needle rides. This is the range that is too lean for best engine performance on stock motorcycles. Either the diameter of the straight part of the needle, or the inside diameter of the needle jet, must be changed to affect mixtures in this most used throttle range. Nearly all riding is done within this off-idle to 1?4-throttle range. From about 1/4- to 3/4-throttle, the taper of the needle controls the main mixture. One normally raises or lowers the needle to fine-tune mixtures within this range. The main jet takes over at about 3?4 throttle and is virtually unimportant below that opening. If you would like to learn more about how to diagnose and tune these carb sub-systems, I invite you to download the Mikuni HSR Tuning Manual (www.mikuni.com; click on the picture of the carb and click on the hot link "Manuals"). I wrote this manual for Mikuni, and although it directly addresses the Mikuni carb, the diagnostic principles apply to the Keihin CV and many other carburetors as well.

To get your Harley's stock carb right, follow these instructions:

l. Buy and install a stock jet needle for a 1988 or '89 1200 Sportster (H-D Part No. 27094-88). This needle was developed for the early Sportster Keihin CV carb that was not equipped with an accelerator pump. As such, it is richer in the off-idle to 1/4-throttle range and works just right.

2. Remove the soft aluminum plug covering the idle mixture screw. Back the screw out to slightly richen the idle mixture (1/2 to 1-1?2 turns will do it).

DO NOT do any of the following:

Do Not change the main jet; the stock one is just right with a free-flowing air cleaner and

mufflers. Yep, the stock main jet is rich. If you find this hard to believe, use the main jet test in the Mikuni manual to see for yourself. You see, the main jet size is not controlled

by emission testing and the government is not very interested in mixtures at full throttle. The factories are free to use any main jet they want and, for some reason, all the stock bikes I have tuned over the past 25-plus years have had somewhat rich main jets, including Evo and Twin Cam Harleys.

Do Not change the slow jet; the stock one is just right with an open air cleaner and free- flowing mufflers. And Do Not install straight, open pipes, especially long ones. If you do, forget everything I've said. Straight open exhaust-equipped engines run poorly in the 2,000- to 3,500-rpm range and no amount of carb tuning can fix that. -- Joe Minton

I've had good luck with it.

From Forum:Between 1/2 turn out and 3 turns out is safe. If you're more than 3 turns out, you need a larger pilot jet, and the danger with running it more that three (more than 3-1/2 or so actually, depending on how new/strong the spring is - call it 3 and be safe) turns out is that the spring cannot hold tension on the screw and it can vibrate out. If you're less than 1/2 turn out, you need a leaner pilot jet.

Idle Drop Method

You need access to this mixture screw to perform the idle drop procedure. It's useful to check where this screw is set before starting the idle drop procedure detailed below. To check the setting, the bike should not be running, then you turn the screw in, one half

turn at a time until it bottoms gently. Keep track of the number of turns or half turns and write this down. Return the screw to the position it was in before you first turned it. It should be between 1/2 turn out and 3 turns out. You also might want to install some baseline jets for your bike's modifications and your operating conditions at this point. If you change the pilot jet, the old idle mixture screw setting will be incorrect. Even if you don't change the pilot jet, the setting of the mixture screw is too lean from the factory anyway, which is the reason we want to adjust it for better performance.

Idle Drop ProcedureBring the bike up to operating temperature. Make sure the enrichener is off. Turn the idle speed down using the idle SPEED adjustment screw (the one by the throttle cables on a CV) until the bike is only barely able to stay running, maybe a little higher than that. 800 RPM is a good RPM if you have an accurate tach. With the RPM lower than normal, you will be able to see the effect that adjusting the mixture screw has.

The idea is to turn the mixture screw in until the idle speed drops, then turn the screw back out until the idle speed drops again, and set the screw in the middle of those two points. What you are doing is making the mixture leaner, so lean that the engine does not like the mixture and runs poorly, then you make the mixture richer until it doesn't like that, and the perfect setting is half-way between the point where is falls off either way.

A couple things to remember1. If the bike gets overheated during this procedure, you will need to let the bike cool off a bit and try again. If you are already at operating when you start this procedure, running more than about 5 minutes while trying to get the setting correct will make the bike too hot. If the bike is too hot when you set the idle mixture, the final setting will be too lean.

2. The screw should be set at least 1/2 turn out from fully seated, and no more than 3 turns out. If it is less than 1/2 turn out from fully seated when it runs best, you should install a smaller pilot jet and perform the idle drop procedure again. If it is more than 3 turns out, you should install a larger pilot jet and perform the idle drop procedure again. If the screw ends up more than around 3-1/2 turns out from fully seated, the spring tension on the screw is insufficient and there is a chance the screw can vibrate out.

3. A tachometer is helpful for seeing the rise and fall of engine RPM if you are not comfortable listening for the changes.

4. The enrichener should be completely off to perform this procedure.

5. An intake leak will foul these results. If the mixture screw seems to have no effect, you may not be able to perceive the change in idle speed, there may be an intake leak, or you may already be either too lean or too rich and you need a different size pilot jet.

Your comments and corrections are welcome.

–Chris

Here is my take on tuning the CV carb for you Sporty:____________________________________

TUNING the LATE MODEL SPORTSTER CV CARB:

It don't matter whether or not your bike is bone stock, or a "Stage 1" .... Stock, the 04-06 bikes run too lean at idle and partial throttle acceleration, but too rich a Wide Open Throttle (WOT). Steady cruise Air / Fuel Ratio (AFR) is the only thing that is correct from the factory.

The Keihin CV carburetor’s idle and just off-idle AFR is controlled by the pilot jet which is fine-tuned with idle mixture screw. Both the pilot jet size and the idle mixture screw setting are important for a proper idle and throttle “tip-in” … thus eliminating the majority of “carb farts” most of these bikes suffer from.

Be advised that the 04-06 bikes suffer from too little timing at idle and off-idle. This contributes greatly to the "carb fart" problem many of you have. The "fix" for this would be to install the TC88A adjustable ignition module which more timing can be programmed into the advance curve.

During 1/8 to 1/4 part throttle and steady cruise, the fuel mixture is controlled by the straight-diameter part of the needle together with the inside diameter of the main jet in which the needle rides.

From about 1/4 to 3/4 throttle (during normal acceleration), the tapered part of the needle controls the mixture. This range is also too lean for best engine performance on stock 04-06 XLs and can be fixed with either the thinner Dynojet needle or shimming the stock needle.

The main jet by itself takes over at about 3/4 throttle and WOT operation since the needle is then completely pulled out of the jet. ______________________________________

1. Fix the idle and off-idle lean condition with the 45 pilot jet. Set the idle mixture screw to 2 1/2 turns.

2. Fix the part throttle lean condition (during normal acceleration) with the thinner Dynojet needle or shimming the stock needle. If you use the Dynojet kit, the C-clip should be installed in the 3rd notch from the top. The 3 washers provided in the kit need to be placed above the C-clip per the instructions. If you elect to use the stock needle, place a total of approx .030” shims (small M4 washers under the needle).

Note: Shimming the needle much more than .030" will kill cruise fuel mileage.

3. Install a 170 or a 175 main jet to fix the overly rich AFR while operating at WOT. A stock 04-06 XL1200 has a 180 main jet. This change in the main jet will also gain HP at WOT.

Note: This combo of the now smaller main jet, but re-calibrated needle will maintain the correct AFR and fuel mileage during part throttle steady cruise.

4. Drill the slide hole: On the bottom of the slide are two holes. The center hole is for the jet needle. Don't mess with it. The second hole is off-center (see photo below). This is the vacuum port. This hole needs to be drilled out just slightly with a #29 metric drill bit. This step will allow for a slighty “snappier” throttle response.

5. Leave the stock slide spring in the carb. If you are using the Dynojet kit, the spring that is provided is too light and will cause carb farts and possibly some surging during acceleration.

6. Make sure there are no vacuum leaks, and make sure the slide diaphram is fully seated in the groove prior to installing the carb's top cover.

7. After the carb is all put back together ... with your finger, move the slide fully up. Make sure it falls back down freely. Just make sure the slide and needle assembly are not jammed.

_____________________________________

Note: Proper AFR on the dyno when at WOT should be between 12.7 -1 and 13.0 -1

If your AFR is not correct at WOT while on the dyno, make a change of the main jet.

getting nice results w/ N65C needle.

I can't seem to stop tinkering with my Sportster. It reminds me of one of those model cars I had as a kid except I get to ride this when I put it back together.I jetted my bike with a few different combos before settling on a 45 pilot and a 175 main along with .40 shimmed stock needle, slide drilled to 7/64 and 2.5 turns plus 1/16. I think this is as close to perfect as it can get. Thats when I start experimenting. I removed the needle and shims and dropped in an 88 needle. kept the same jets and re set the A/F mixture. I really like this change. The bike runs every bit as strong except smoother, more linear like. The different circuits are brought together seemlessly with this needle. I know the needle plays no role in the starting and idling but thats better too most likley due to re setting the A/f. The one thing I may try is a 170 main jet. I tried 180 and the bike could not reach as high a top speed within the same distance as it did with a 175 .If It improved with the 175. It may well get even better and like a 170. We shall see.Iv'e read posts from felow XLF members regarding the N65C needle. Some like it, and some... not so impressed. So I thought I would share my own experience. It's a keeper.Well until I can get my hands on a Mikuni. __________________06 1200R. S model Cartridge forks/ remote resevoir shocks, Superbrace, SE cams, Twin-tec ignition, 28t final drive, Modified BS II intake, CS exhuast w/ Crims baffle mod

On my 05 883C I had SE II slipons. NHRS hurricane a/c. 42/175 jets. N65c needle. No shims.

This setup worked well, except occasionally I still had carb farts. So a couple of days ago I installed a #44

(yes, a 44), slo jet. This was the ticket to a smooth, great running 883. My setup is now:

SE II slipons.NHRS hurricane A/C.44/175 jets.N65C needle, no shims.2 1/4 turns mixture screw.

The #44 slo jet is a Drag Specialties after market jet. Order from a dealer. This 44 is about half way between the 42 and 45 jets. Perfect.

Jim

2004 1200 C48, 175, N65A needle shimmed with a Ram-flo 400 and Gronk's mod stock pipes. Bike picked up about about 3 hp and 7 lbft over 45, 175, needle not shimmed and 49 state pipes. __________________Dave

Performance and Efficiencyby Joe MintonAmerican Rider

Email this article to a friend!

Many readers have been asking questions that nibble around the edges of the subject of gasoline and how our Harley engines use the stuff. Since we seem to be in for high gasoline prices for the indefinite future, this seems like a good time to practically consider gasoline usage in Harleys.

For years I have known that a great majority of Harley owners do not consider the cost of gasoline to be very important. Also, mileage has seldom meant much to this majority. If there has been a concern, it has been about range-how far one can go on a tankful. For a number of very good reasons, including cost, morality, and national security, these attitudes are changing. With that said, let me get practical and perhaps somewhat blunt.

I'll be first in line to say that stock Harleys could use more power, especially in the middle part of their rpm range. However, it is a myth that reduced mileage and efficiency are inevitable companions to improved performance. Quite the opposite can and should be true.

An engine with an aftermarket exhaust and air cleaner, but with stock motor parts, should produce mileage close to what it delivered when it was still stock. If it does not, the carburetion (or EFI) is out of tune.

A stock Big Twin normally delivers around 40 to 42 mpg at 65 mph on a flat windless road. The same bike with our 88/95 conversion should get at least 10 percent better, while delivering 40 percent more torque at cruise speeds. I have had many Harley owners tell me that they are getting 49 to 51 mpg at steady interstate speeds with this engine conversion.

How can this be, you ask? It's simple, really-an appropriate cam design, higher compression, and a free-flowing exhaust and air cleaner together with correct air/fuel mixtures.

Most Harleys are modified in ways that affect fuel mileage. Owners normally change to more open (louder) and less restrictive exhaust systems and air cleaners. Both of these modifications have an effect on the air/fuel mixture strength; they make the engine run leaner. Stock bikes are already rather lean for emissions purposes. Air-cleaner and muffler changes further lean the mixtures, so much that correcting this is necessary for the engine to run well.

Unfortunately, these mixture changes are normally done incorrectly. The result is an engine that, although it doesn't melt down from being too lean, runs rich enough to give less-than-optimum performance and fuel efficiency-especially at higher elevations.

Maybe you own one of these bikes. Does it start to miss and emit black smoke at a few thousand feet above sea level? Is there a hard hesitation when you roll-on the throttle from interstate speeds? Does it deliver less than 40 mpg at 65 mph? None of this has to happen. If the mixture alterations have been made correctly, your bike should run better than stock, not worse.

Stock Harley Big Twin and Sportster engines, both the carbureted and EFI versions, are tuned to be EPA-lean in the lower half of their throttle range. The result, especially with the carbureted engines, is flat mid-throttle acceleration. Very little alteration is required to correct this.

The stock Keihin carburetor is a fine instrument. It is reliable, long-lived and easy to tune-if you know how and use the right parts. Because Harley has used the Keihin for more than 15 years, there are enough alternate tuning parts lurking in The Motor Company's parts books to make do quite well.

All the Keihin carb needs to deliver proper mixtures for stock and modified engines is a different needle-one that your Harley dealer can easily get from The Factory-and a simple adjustment.

The needle I have used and recommended since 1990 is the needle from the first (1988-89) 1200 Sportster, Part No. 27094-88. This needle is smaller in diameter (richer) in its straight-diameter section, which controls mixture strength in the 1/8-1/2-throttle range. Buy it and install it.

You also need to open the idle mixture screw about one turn (adjust for best idle). You do this by removing the soft aluminum plug covering the screw on the bottom of the carburetor.

The main jet seldom needs changing because the stock jet is about two sizes too large. An open exhaust and air cleaner makes it just about right. This jet only becomes effective at throttle openings of 3/4 and above, so unless you ride at wide-open throttle all the time you needn't concern yourself with the main jet.

EFI engines are also tuned to be rather lean in the 20 to 40 percent throttle range. They seem to be more accurately adjusted at idle. There are a number of aftermarket EFI tuning kits that allow richening the mixtures in this range. I have experience with the Power Commander and recommend it.

If you take this information to your mechanic, factory or otherwise, there is a reasonable chance that you will meet resistance to my advice. Harley sells carburetor kits and everybody is a carburetor expert. Normally, I would recommend Harley parts because I have some knowledge of how hard they try to get things right. The Motor Company's jetting kits, however, are an exception: they deliver very rich mixtures and wear out quickly. Many, many of you have one of these kits installed in your carburetor and are getting mileage as low as 26 mpg.

The needle and needle jet in these kits are made of brass; the stock Keihin needle is polished hard-anodized aluminum, and the needle jet is hard brass. The brass-on-brass of the kit wears quickly and further richens an already too-rich mixture. The stock parts hardly wear at all. I have examined stock needles and jets with 45,000 to 70,000 miles of use and could not detect measurable wear.

A majority of mechanics change the slow (idle) jet to a larger size in an effort to richen the mixtures in the lower throttle range. I think they do this mostly because they don't know about the importance and effect of the needle's diameter above the taper (the straight part). If you can get your mechanic to try what I have suggested, he can see for himself, and the resulting performance improvement will convert him.

By the way, if you use a Mikuni on your Harley, buy and install the "mileage" or "lean-out" kit. Mikunis are also tuned too rich. Fox Distributing in Illinois (630-513-9700) sells this kit (the parts are genuine Mikuni). It improves mileage, throttle response and engine smoothness. Also, go to www.mikuni.com and download the tuning manual if you don't have it.

I have several reasons for going on this long about air/gasoline mixtures. First, I want you to get the most out of your ride, and I know many of you are riding poorly tuned machines. Second, it is time we consider efficiency and not just power. Third, I know and have proven many times that it's possible to have both power and efficiency.

Finally-I guess I am getting old and crotchety-I no longer feel any obligation to not offend factories, suppliers, dealers or poorly informed mechanics. Gasoline and its efficient use is simply too important for such niceties.

»More V-Twin Tech

Taxes Paid...Lessons Learned

First of all I would like to thank everyone in this forum for the great info that got me through this project. The only drawback was the amount of searching required to find all the info. I wanted to try and consolidate as many of the tips as I could into one post to make it easier for anyone else who is doing Stage I for the first time. I just want to make it clear that 99% of this I found here from other people.

I bought my '04 XL1200C in Sept. of '05 and after my first weekend realized that I had to upgrade the exhaust to the SE II slip ons. I planned to get the SE A/C and have the local dealer rejet but I didn't want to pay them to do it. Eventually I saw the hyperchargers and thought I needed one but I lost that urge after a couple weeks. Then I saw the setup on honus402's bike and decided that was what I had to have.

I bought the Arlen Ness Big Sucker ($90 on ebay), the A/C cover for bt's from the skull collection ($39 from h-d), a chrome carb cover ($16 at h-d), Sorgy's jet kit (ebay $11) and some stainless steel M4 hex socket cap screws, flat and split washers as well as a couple thinner (.025") M4 brass washers to shim the needle.

Here's the lessons part:

1. Use a blanket or towel to protect the bike, catch loose parts and soak up extra fluids.

2. Once the air cleaner is removed the carb will come loose from the engine if you grab it on top and bottom and rock it up and down. It is held on to the intake manifold by a rubber gasket. When it comes off make sure to keep this gasket on the intake and not the carb. This will make it easier to put the carb back on later.

3. Replace the stock phillips head screws with hex socket head. It is too easy to damage the phillips head and some nice stainless will look better. The Sorgy's kit comes with 4 for the bottom and I bought 4 more for the top.

4. Replace the stock plastic cover with a chrome cover. This isn't really necessary but it looks great. The screws that come in the Sorgy's kit are a little too short for the right rear because it has to go through the throttle/idle cable bracket before the cover. All of the screws are M4 but I don't remember the lengths.

5. Remove the screw holding the throttle/idle cable bracket to the side of the carb. Once you have the cap off it will make it a lot easier to get the diaphragm seated correctly if the arm of the bracket is out of the way of the cover.

6. Very important!!! Make sure you are extremely careful with the rubber diaphragm in the top of the carb. If you are replacing the needle or just putting washers under it you have to first remove the slide assembly which includes the diaphragm. Don't pull on the rubber part, push the slide up from inside the air intake until you can grab it from the top. When you replace it make sure you don't pinch the rubber under the cap. If the cable bracket is out of the way you shouldn't have any problems. It costs about $43 to replace (don't ask how I know that) and cuts easily so take your time and wiggle the cap a bit to make sure you don't pinch it.

7. If you are using a Ness Big Sucker, wipe a little petroleum jelly on the four o-rings to help keep them in place. They fall off easily and get lost just as easily (again, don't ask). If you do lose one, go to an automotive parts dealer and get a bag. Some people have mentioned using a thicker ring but the stock ones are 1/16" wide, 5/8" inside diameter and 3/4" outer. The directions are also very vague about the o-rings placement. Two go on the back side around both of the large banjo bolt holes and two go on the front side.

8. The Ness directions talk about installing restrictor bushings. The newer kits have different banjo bolts so if your kit didn't come with them you don't need to install them. The hole is the right size already. The directions also talk about re-routing the breather hose. On my 04 the hose was already where they tell you to run it.

9. Replace the carb the same way it came off. Make sure you have the rubber gasket seated properly on the intake, press the back of the carb into the gasket and rock the carb up and down pushing into the bike. When you fit the air cleaner plate you can tell if you are close with the carb or if you need to push more.

10. Second most important tip, make sure you have and are using the proper tools.

11. Most important tip IMO, try to learn something. If you are doing the job yourself you might as well look around and see what is going on in there.

I hope this helps the other new wrenchers out there. A lot of other threads have more details and better directions so keep searching and good luck. In the end it is worth it to know that you did the work yourself even if it costs you an extra $43 cause you screwed up. I am not a mechanic and don't consider myself an expert so if anyone has any corrections or additions please feel free to add. I think that's the whole idea behind a forum anyway.

SECRETS OF THE DYNOJET KIT REVEALED

By: Chuck Antolina

Let me say up front that I have never really given the design of each carburetor any deep thought. I always went with the principal that whomever designed it, knew what the hell they were doing. My job was simply to keep it clean, and balance the fuel/air ratio in the manner prescribed for each unit. There came the really fun part. Tuning. Because of my classical music training, and eventual training as a live audio engineer, I found I could pick up on the slightest of nuances that occurred when even tiny changes were applied in any case. I believe that is the key to street tuning for me; without any equipment.. Are there

better ways? Absolutely. But for me, this just works. Trust me when I say I do not consider myself an expert, by any means.

I bought my first Harley last year. It was a 2002 XLC 883. Lots of bling-bling, not much else. There were SEII’s on her, but the jetting had never been touched. On this bike, I learned loads about the CV carb; how it worked, the stages, and how they interacted. With the help of my friends on XLFORUM.com, I soon became quite adept at tuning my bike. And I haven’t stopped dickin with the CV carb since….

Recently, I bought a 1997 XLH, in great condition, and very close to stock. Perfect. It was clean enough to eat off of, and nobody had been dickin with it too much. What a deal.

My first project, of course, was to do the “Stage1”. Roxy had stock exhaust when I met her. I naturally assumed that she was “bone-stock”. I swapped out the stock exhaust for the SEII’s salvaged from my previous bike’s life. J I started looking through a box that came with the bike, and noticed a plastic box. In it, were obvious carb pieces that I recognized…sort of. Uh-oh….”What the hell is this?”

This was my personal introduction to: The Dynojet jet kit with the “THUNDER NOZZLE”.

Now, I had heard about these kits on XLFORUM, but was quickly convinced that they were a waste of money. After all, the manufacturer knew what they were doing, right? I was told (and believed) that the CV carb was the closest thing I would ever get to fuel injection. Sounded good to me! (I don’t even want to discuss fuel injection. It makes my head hurt.) Besides, I had tuned my carb to what I thought was “always one step from perfect”. J I could tune a carb with 4- $1.50 jets and my favorite screwdriver (and perhaps my drill, if needed). Who needs to spend real money for that? Insane, said I. But, I digress…

I went back to my beloved XLFORUM, and began quizzing folks on the Dynojet products, and poked a great deal of fun at the marketing concept called “THUNDER NOZZLE”. Even today, I can’t help but type that in caps. Still makes me giggle. J

Admittedly….I was pissed off. It seems the emulsion tube was redesigned in this kit. Along with that, the main jets were a different threading. No more jets from the dealer. If I didn’t have one, I HAD to get one from Dynojet. NOT cool. And, may I say still to this day: NOT COOL. Then again, what was I to expect? This was a kit, fer God’s sake. If you knew and could tell the difference between a 180 and a 185, you probably didn’t buy the kit, anyway. J So, I guess my anger was mostly directed at the previous owner- a “professional mechanic” for 15 years. Oboy.

Well, as I said earlier, I don’t know a lot about carb design, but I DO know that with a redesigned accelerator pump nozzle, redesigned emulsion tube, and a redesigned slide, and the drilling involved in the installation of the kit, what I knew about CV carburetors soon seemed suddenly very minute. Since I didn’t know where “zero” (stock) was anymore, I had lost ALL sense of reference in the manner of properly tuning this carb.

Now, I’m a pretty fart smeller, but not smart enough to know when to shut my mouth. After enough bitching, Stevo responded with this:

“So Chucky .... explain to us what the differences are between the stock parts and the Dynojet parts and what areas they affect and what those effects will be.This is your homework assignment....and I expect it to be right......now go and do some research......'cos when ya write it all down the answer will magically appear.....

So, here it is, my homework assignment. Feel free to post your thoughts, opinions, arguments, whatever. I have a big mouth, and I don’t really give a shit what you think. Oops, I mean, civil discourse is always appreciated. Yeah, That’s what I meant. This was more for myself than anything, but I’m always willing to share….well, because I say have something to say, and yer damned well gonna listen.

By my research and by physical inspection, I found the following design differences between each change. A little later in this article, I’ll attempt to explain what has happened, as a result, to the overall operation of the carb, as changed from stock.

• Redesigned Slide Needle/Spring-The new Dynojet needle is made of a somewhat lighter metal, and coupled with the lighter spring, and the drill mod to the vac-port (bit included) it was designed to respond more quickly. Drilling out the vacuum port allows more volume from the vacuum system (Essentially making the slide spring relatively “heavier) Hmmmmm…..

• Redesigned Accelerator Pump Nozzle-This nozzle has a slightly larger opening in towards the carb throat. Also in this redesign is a roller-type nozzle actuator. Together, their job is to put more fuel in the throat of the carb during acceleration. Hmmmm……

• Redesigned Emulsion Tube-The only visual difference I can see in the emulsion tube is a slightly larger circumference, and LOTS fewer “emulsion holes”. The theory is that this emulsion tube somehow more efficiently mixes fuel with air at the “emulsion stage”, when fuel is vaporized and mixed with air to aid in combustion (one of the real marvels of the CV carb, IMHO). Hmmmmmmmm……

Ok, now that we see what has been changed, let’s talk about the net effect:

The pilot system is unaffected by the Dynojet kit, physically. There are no mods in this section. That’s good, because the pilot system is too important (and really, too basic) to change anything other than jets, anyway. The real differences start to show up in the mid-range, which is affected by the slide and needle.

Now, they have us change out the spring to a lighter one, and then have us drill out the vac-port, effectively making the spring “heavier” (by the change in pressures). OK, whatever…more parts, bigger box. I guess it makes sense to let the changes in pressure on both ends be more important than the physical weight supplied by the spring….do both, or do neither, don’t do just one.

Of course, you can change needles on any CV carb, but the one from Dynojet comes with a handy set of rings and circlips, for shimming the needle to different heights, thereby allowing for richer or leaner settings in the midrange. The real difference in the dynojet needle, tho, is the taper. Here is a comparison of the stock needle from my bike, and the dynojet needle:

Although there is only a .001 in. difference in base diameter before tapers, the length of the Dynojet needle is increased somewhat. This adds to its adjustability. It also has slightly larger diameters thru most of the length of the tapered part of the needle, yet ends in a .029 in. smaller tip diameter. Very quick reduction in taper near the end...

Now, if you have a THUNDER NOZZLE installed, make sure it points in the right direction. It should face the carb drain with the bowl removed. Essentially, this nozzle adds more raw fuel to the carb when accelerating. There’s a good reason for this. Read on.

The most baffling change in design, to me, has been the emulsion tube (which holds the main jet). Its job is to vaporize fuel and pre-mix it with the air to aid in more efficient combustion. Brilliant, may I add. J The baffling part is that the dynojet emulsion tube has only 2 tiny holes in it. I’m gonna go out on a limb here, (remember, I’m no expert) and say that the fewer holes, while allowing less VOLUME of air to enter the venturi, significantly increases the SPEED of the mixing…with only 2 holes, the air moves faster, thereby actually enhancing the emulsion effect, and moving the combined gas/liquid emusion at a much faster rate....I could be wrong…I’ve been wrong before… J The thing to remember is that the needle’s job is to somewhat interfere with the “swirling” in the venturi…it does this more smoothly when the air is coming from only one point (or two really, but in the same vertical plane)

So, as it all comes together, you can notice that as much as it’s changed, it’s stayed the same, really..The only changes are how the volumes of fuel/air are delivered after the pilot circuit…and when. And those will be primarily dictated by the changes one makes in the slide mechanism.

The pilot jet controls the idle, and continues working throughout the spectrum. Upon acceleration, the larger accelerator nozzle adds more raw fuel than is typical, partly to make up for the increased air flow because of the vacuum changes, and partly because the quicker needle will add more fuel to early midrange sooner, but not quite soon enough to settle the leaner condition. So, as the midrange opens up, the needle starts to handle the lion’s share of midrange, until you reach 3/4 throttle, where the main jet is pretty well wide open. Personally, I would recommend going with the smallest main jet you can get away with when using the dynojet setup, as there is a possibility of wasting fuel (and HP) on the very top end.

Stevo's Jetting 101 is STILL the be all, end all, in understanding HOW to tune IMHO. I refer to it quite often, and learn something new every time…If you haven’t read it, please do, and THEN come back and read this….and argue with me, please….I’m no expert, I’m just doing a homework assignment. And I have SO MUCH more to learn….

and, Thanx, Stevo

(EDIT...had a few problems with this post...a little too long....had to chop a good deal of this post to make it fit...Stevo's link is ok now....still can't make images embed...not sure why..)

Second edit: This was not a Thunderslide kit, as Shu pointed out, and he is right, so I fixed it....

p From Cold ..............................5 - 6 Parts Air : 1 Part FuelAcceleration (Max Power)1/2 - WOT.........Around 12.5 : 1Idle - 1/8............................................. Around 12 : 1Twisties 1/4 - 1/2..................................Around 13.5 : 1

Cruise 1/8 - 1/4...................................Around 14.7 : 1

I Have Found That With Later HD's (And This Covers Sporties And Big Twins From About Mid '90's) That The Main Jet And Needle Are Very Close To Correct.The Main Problem Area Is The Pilot Circuit Is Too Lean In Most, Not All, Instances..An Increase In Pilot Jet Size By One Size Is Usually All That Is Needed...Sometimes 2 Depending On Intake And Exhaust And CamsThis Means If Your Bike Has A 40 Then Go To 42, 42 Then Go To A 45, 45 -> 48

At The End Of The Day A Carb Does Nothing More Than Meter The Fuel... The Motor Doesn't Care What The Carb Looks Like Or What Jets Are In There.....So Long As It's Getting The Right Fuel Air Mix For The Conditions...

Here's A Few Symptoms/Fixes

When Trying To Tune A Bike You Need To Know What Circuit Is Covering The Area Where You Feel You Have A Problem.Changing The Main Jet Will Have No Effect On The Idle And Up To 1/2-3/4 ThrottleWhereas A Part Throttle Problem That Requires An Increase In Pilot Jet Size Will Give A Little Extra Fuel Over The Whole Range

If You Have Had The Carb Off Then Check The Float Level ....You Will Need To Refer To Your Factory Manual.... But A Very Close Guide Is The Join Line In The Floats On The Square Float Models Should Be Parallel To The Base Of The Carb When The Carb Is Held About 15* From Vertical.

---------------------------------------------------------------Idle - 1/8 ... Pilot Circuit

Signs Of Too Lean

If The Bikes Surges Back And Forward At A Steady Throttle At Around 3000+ RpmExcessive Popping Or Backfiring At Closed Throttle Deceleration..The Bike Runs Better When Hot But Still Not RightIf You Blip The Throttle From Idle And As It Drops Back Down To Idle It Tends To Hang Up A Few Revs Too High And Then Come Down To A Lower Rpm...

Wind Out Pilot Screw By Half A Turn At A Time And See If It Improves.... If You Get Past 3 1/2 Turns Then Go Up To Next Size Pilot Jet

Other Things That Will Give A Lean Condition Are Intake Leaks..... If In Doubt Then Replace Intake Seals And Lube Them With A Silicon/Rubber Grease As They Are Assembled...

Sign Of Too Rich

Sooty Plugs..... Too Large A Pilot Circuit Will Soot Your Plugs Up Way More Than A Rich Main CircuitThe Bike Runs Better When Cold But Still Not Right...If The Bike Doesn't Require Choke To Start And Idle From Cold Then You Are Too RichIf The Throttle Is Blipped From Idle And The Revs Drop Below Normal Idle And Then Come Back Up To

Normal Idle....This Will Be Worse When The Motor Is Hot.

To Correct... Wind Pilot Screw In 1/2 Turn At A Time ... If It Gets Less To Only 1 Turn Out Then Reduce The Pilot Jet By One Size

----------------------------------------------------------------

1/4 - 3/4

This Is A Hard One To Pick........Try Running In 2nd Or 3rd Gear And Crack The Throttle...

If It Pulls Clean ... Leave It....It Takes A Lot Of Experience To Pick The Difference Between A Rich Or Lean Condition Here...

I've Found That Needle Heights From Standard To About 0.030" Raised Is The Range For Most...This Is Done With A Small Shim Under The Head Of The Needle...Make Sure That The OD Of The Shim Is No Larger Than The Needle Head Or The Needle Will Not Sit Properly And Will Float..

A Lean Condition Will Tend To Surge Or Feel Flat.... A Rich Will Tend To Feel A Bit Soggy...

Try And Take Notes On The Weather ... If It Is Better When The Motor Is Cold Or When You're At Sea Level Or The Ambient Temp Is Lower Then You Are Probably Rich

If It Is Better When The Motor Is Hot Or You're At A Higher Altitude Or The Ambient Is Higher ...Then You're Probably Lean

--------------------------------------------------------------

Wide Open Throttle .. WOT

A Main Jet Guide To Rich Or Lean ...

A Few Points ... Your Lower Speed Circuits Tend To Work More Off Vacuum Than Airflow..... Whereas The Main Jet Or WOT Tends To Work Off Airflow.

WOT Throttle Runs Are Best Done At The Drag Strip And You Want The Jet That Gives The Best Mph Thru The Traps...... I Prefer To Start Rich And Come Back Down While The Mph Keeps Increasing Until The Mph Drops ... Then Go Back Up A Size...But Ya Can Start Lean And Go Up One Size At A Time Until The Mph Drops And Then Come Back One Size..

If It Runs Better At Night .... Ya Probably Rich ... If It Runs Better In The Afternoon, Ya Probably Lean..

If You Don't Have Access To A Drag Strip Then A Dyno Is Good For WOT Runs But Not Very Good For Part Throttle Runs Unless You Have A Good Operator..

Without Access To A Drag Strip Or Dyno, Here's A Few Tips..

As Stated If It Runs Better When It's Cold Ya Probably Rich.....If It Runs Better When It's Hot Then Ya Probably Lean....

Another Way Is To Take It Past 5000 In A High Gear At WOTThen Close It To About 7/8 Throttle

If The Engine Accelerates A Touch Then You Are Lean....If The Engine Hesitates, Then Ya Probably Rich...It Should Just Slow Slightly...

If The Engine Pops At The Change Rpm At Full Throttle Thru The Gears It Is Usually Lean.

Another Guide For Rich/Lean ...

If You Remove The Air Cleaner And The Bike Improves Then It Is Probably Rich

If You Tape Up Half Your Air Cleaner Element And It Improves Then You're Probably Lean

Turn The Fuel Tap Off And Keep Riding...

If It Improves As The Fuel Level Drops, Then It's RichIf It Gets Worse As The Fuel Level Drops Then It's Lean

If It Runs Better In That Range When The Air/Motor Is Cold It's Rich

If It Runs Better In That Range When The Air/Motor Is Hot It's Lean

Read This First ----- Jetting 101

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Jetting A Sporty

A Carby Works By Mixing Air And Fuel Into A Vaporous Mixture.We Want The Ideal Mixture So The Bike Runs Well.

Unfortunately It's Not Quite Simple...As A Carburettor Mixes Air By A Set Volume To Set Amount Of Fuel.The Amount Of Oxygen Density In That Set Amount Of Air Varies And This Is What Gives Variations In Mixture Due To Differing Conditions.

The Required Air / Fuel Mixture Changes Depending On The Conditions

Max Power For Acceleration Is Around 12.5 Parts Air To One Part Fuel

Chemically Correct Or Stoichiometric Is 14.7 : 1

A Rich Mixture Misfire Usually Needs About 6-7 :1A Lean Mixture Misfire Usually Needs Over 20 : 1

We Want To Try And Get The Most Fuel In There That We Can But The Limiting Factor Is The Amount Of Oxygen That We Can Fit In There And Give The Correct Ratio...

A Number Of Things Have An Effect On The Amount Of Oxygen We Can Get In There..

Just Like You Run Out Of Breath At Altitude Because Of Lack Of Oxygen So Does Your Bike..

The Air Pressure Or Barometric Pressure Is Higher At Sea Level Than At High Altitude.The More Pressure We Have Means The More Oxygen In The Same Amount Of Air

If The Bike Is Jetted For The Correct Mixture At Sea Level And Then You Go Up The Mountains.Then The Higher The Altitude The Less Oxygen And The Richer The Bike Will Run.The Opposite Is Also True.

A Few Other Things Also Have An Effect.

Hotter Air ................................................. = Less Oxygen :- RicherColder Air ................................................. = More Oxygen :- LeanerHigher Barometric Pressure Or Low Altitude....... = More Oxygen :- LeanerLower Barometric Pressure Or Higher Altitude ... = Less Oxygen :- RicherHigher Humidity.......................................... = Less Oxygen :- Richer

One Of Basic Things That People Don't Seem To Understand Is That There Is Different Fuel Circuits N The Carb For A Reason...Different Circuits Are Used At Different Throttle / Vacuum Positions Not Rev Ranges..... The Revs The Motor Is Doing Has Stuff All To Do With Which Circuit Is Being Used.

At Idle And To 1/8 Throttle Is Mostly Used At Cruise In Town And Just Leaving The Lights ...... This Area Is Governed Mainly By The Pilot Jet And Pilot Screw..... Although The Parallel Portion of the Needle Can Supply a Bit of Fuel Too

Highway Cruise Is Around The 1/8 - 1/4 Throttle Depending On the Speed You're Doing.....This Area Is Governed By The Pilot Circuit And The Needle..... The Start Of The Taper On The Needle Starts To Come Into Play Significantly Here

Pushing Thru The Twisties Tends To Use The 1/4 - 1/2 Throttle This Area Is Mainly Covered By The Needle But Both The Pilot Circuit And The Main Jet Have A Small Input

1/2 - Wide Open Throttle ... Hard AccelerationThis Area Is Covered By The Taper Of The Needle And Then The Main Jet Becomes The Main Fuel Supply From About 3/4 Throttle To WOT

A Few Points.. The Pilot Circuit Supplies Fuel Throughout The Whole Range

Jetting and Fuel Injection Adjustment, Pipes By Scott Holton, J&P Tech Regardless of whether your bike uses a carburetor or fuel injection, the correct fuel air mixture is important. Any changes to the intake tract or exhaust system can impact the Air/Fuel mixture.

Whenever you make a change in the airflow through the engine, changes can occur in the fuel / air mixture on your bike. Bad conditions that we need to correct are running either too lean or too rich. Running lean can burn pistons, score cylinders...running rich fouls plugs and runs bad. Changing the air cleaner or the pipes changes the mixture. Changing baffles also changes mixture. With a carbureted bike, the fix is to just change the jets. With a fuel injected bike it's easier, the fix is to install a Power Commander (see Carb section of the J&P® catalog for jets and Power Commanders). Carburetor jetting is very complex. Factors such as humidity, altitude, and air temperature, all affect the ratio. With a carbureted bike, if you have a Dyno and an exhaust gas analyzer, the adjustments are very easy and straightforward. To change to the correct jet, you must understand where the jets are effective. We will discuss the CV carb that came on Big Twins from 1990 through 2004 and XL's 1988 to 2004. On a CV type carb, the pilot jet and idle mixture screw control throttle position is up to 1/4 open. The midrange is controlled by the thin needle position in the slide, and 3/4 throttle and up is controlled by the main jet. The correct Air/Fuel ratio is about 14.7 to 1, or 14.7 parts air to one part fuel. Without an exhaust gas analyzer, you will need to make an adjustment and read the spark plugs (check plug color) to determine the effect. The desired color is a very light tan to chocolate brown. Here is a basic procedure to determine what jet to change. First, change the components such as pipes or air cleaner and get yourself 3 or 4 sets of new plugs, gapped and ready to install. We need to have access to the idle mixture screw, so we need to drill out the plug covering it. Once this is done, screw it in until it bottoms lightly, then back out 11/4 turns. Put a piece of masking tape around your throttle. Pick an easily seen reference point on your switch housing and mark on the tape where the zero (0) throttle position is. Open the throttle wide open, and mark on the tape the full throttle point. Half way between these marks mark again, and divide the 2-1/2's in 1/2 again. When you are though, you will have a mark at 0, 1/4, 1/2, 3/4 and Wide Open Throttle on the throttle sleeve. Next, start the bike and warm it up so that it idles without the use of the enrichner. Once that's done, while wearing a set of mechanics gloves, remove the spark plugs and install a new set. Take the bike out and ride it for about 10 to 15 miles at 1/4 throttle if possible. Things get a little complex now, so pay attention. We need to do what's called a "plug chop". This is where you pull the clutch, kill the ignition, and pull to the side of the road (carefully of course) WITHOUT ALLOWING THE BIKE TO IDLE. Still using your mechanic gloves, remove a plug and look at the color. If they are black and sooty, you are running rich on the pilot jet and need to reduce the amount of fuel by installing a smaller jet. If they are clean white, you are lean and need to give the engine more fuel by using a larger pilot or turn the mixture screw out a 1/4 turn. If they are brown no change is required. To aid in tuning, when you go in with the mixture screw, you get a leaner mixture. Out you richen the mixture. As a general rule of thumb the idle mixture should be 1-1/4 to 1-1/2 turns out when you have selected the right pilot jet. Repeat your test with fresh plugs for 1/2 throttle. Here in order to make a change, we can add fuel only with a stock needle by shimming with tiny washers under the needle. Every shim you add richens the midrange. The Dynojet tuner kits are equipped with a needle that has grooves in the end to adjust the position with a clip. Remember the higher on the needle the clip is the leaner the midrange becomes. Install the appropriate jet you have decided upon (or make needle change), and a new set of plugs and redo the test. Repeat this until you have the correct light chocolate appearance. The main jet is your cruising jet and needs to be tested above 3/4 throttle. It requires nice stretch of open road, or better yet a drag strip. Repeat the same type of test as before at 3/4 throttle and full throttle, doing your plug chop. Make changes accordingly. An additional test that is handy is to get up to, fourth gear at about 4000 RPM. Open the throttle all the way then immediately let off the throttle about 1/8. If the engine slows just a bit, the jet is close, if it seems to pick up speed or RPM; the main jet is too lean. If it hesitates or stumbles, the main is too rich. Change jets and test again. After you have the jets close, I just ride about 50 to 75 miles observing the performance of the bike at different speeds. Poor acceleration, pinging, knocking, surging and popping or spitting through the carburetor suggests you're still lean. Black smoke, sooty exhaust, smell of unburned fuel and a rough idle suggest too rich. When I get back from the ride, I pull the plugs once more and see what I've got. If they are tan, light chocolate and the bike runs good, I'm done. With the Power Commander, things are slightly different. With a PC you will need to access the Power Commander website, www.powercommander.com, and select the map that is closest to your combination. This must be downloaded into your Power Commander. If the bike does not run well determining your needs are very similar to the tests outlined above. Mark your throttle, do your plug chop,

read the plugs. Unfortunately it is a little more complex to make a change. Accessing the map in the Power Commander, you can change cells in the map to richen and lean. This is a simplified version of tuning the Power Commander but it should give you an idea of what's required.