Harley cv carb jetting chart

Main Jet. Pilot and Main Jets. As you can see, Harley carburetor jetting is a fairly simple procedure that under most conditions will yield greater performance when requiring a richer fuel mixture. Enjoy the Ride! Main jet replacement should be reserved until after the slow idle jet is replaced and mixture is tuned unless a lean condition is apparent during full throttle. Harley carburetor jetting can be accomplished with minimal mechanical knowledge.

Tools to perform this task include just a simple set of screwdrivers.

harley cv carb jetting chart

Remove the 4 screws securing the bowl to the base of the carburetor and remove the bowl. The jet size is stamped into the top of the jet i. Be careful not to strip the head of the jet. Pilot Jet location. With a flat head screwdriver unscrew the Main Jet from the brass needle jet holder aka Emulsion Tube. Note the jet size stamped into the top of the jet i. There is no need to remove the emulsion tube unless required for cleaning. Replace the Pilot Jet with one size larger.

This of course assumes that you are starting out with the stock jet size.

harley cv carb jetting chart

If your stock jet was a 42 the next size larger will be 44 or Only increase the jet sizing one size at a time to avoid an overly rich idle. Main Jets are sized incrementally by 5, so if your stock jet was a the next size larger will be Avoid installing jets that are too rich as this will create a sluggish feeling at full throttle as well as contribute to plug fouling.

Many Twin Cam models except California are already appropriately jetted with a main jet that will allow for a good starting point for tuning. As mentioned, proper mixture adjustment is key to proper jetting and should be performed first. Reinstall the bowl making sure to align the accelerator pump shaft and rubber boot.Note: If your engine does not start or idle properly now, you should attempt determine the cause and repair it prior to making these carburetor modifications.

Do not under-estimate the ability of the stock Keihin CV carburetor to produce good horsepower. The stock CV carburetor has a venturi diameter of 40mm 1. A stock bike cc 80 CID can develop up to 64 horse power with a well tuned and modified CV carburetor.

Click here to see dyno testing on the CV against other carburetors. With a few parts from your local Harley-Davidson Dealer and some tools, you can re-jet a CV carburetor and improve the performance of your bike. Slide Spring 2. Slide Diaphragm 3. Vacuum Slide 4. Vacuum Port 5. Needle Jet 6. Main Air Jet 7. Main Jet 8.

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Slow Jet 9. Idle Mixture Adjustment Screw Throttle Plate Step 1. You might get away with leaving the throttle cables connected. It is much easier to remove the carburetor and use a work bench. It is faster to cut the fuel line hose off rather than trying to save it.

If you take out the rear fuel tank bolts and loosen the front bolts, the fuel tank can be raised a few inches. The extra room gained by raising the tank is the difference between struggling with the job and making it easy. The aluminum plug covering the idle mixture adjusting screw needs to be removed. Turn the carburetor over and locate the plug toward the rear of the carburetor, in back of the float bowl. If the plug does not fall out while drilling, remove the drill bit.

This will allow enough grip to remove the plug by pulling on the self-tapping screw with a pair of pliers. Underneath you will find a slotted screw. Over tightening this screw can damage the carburetor and needle. This provides a starting point for tuning.Every carburetor know to man will have a way to adjust the air fuel ratio at idle. This adjustment will trim the mixture so that you can have a smooth running engine.

They work opposite of each other so it is important to know that before performing this procedure. What you are after when adjusting this screw, is too reach peak idle RPM and smoothness. This is the engine telling you it is happy, and it runs best at this mixture. The pilot jet is sized correctly if the air screw setting falls between turns out, with 1.

A pilot air screw will be made of brass, gold in color, and will have a blunt tip compared to a pilot fuel screw.

How to Adjust a Harley CV Carburetor

I use the smallest diameter screwdriver so I generate the least amount of torque. A pilot air screw will be located on the air box side, while a fuel screw will be located on the engine side. This is true for most carburetors. When in doubt, remove the screw and see what kind of tip it has, that will determine what it meters. This video walks you through removing them.

Now, adjust between these two settings to achieve highest RPM and smoothest running engine. Reset idle to recommended settings and test ride motorcycle.

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If they dip below idle, lean the mix. When you close the throttle and decelerate, the engine runs lean, and can pop through the exhaust. Sometimes this is considered normal with a race engine and open pipe. Hi, this website is very helpful for me.

harley cv carb jetting chart

Thanks before. But i have an issue on my mikuni bs.Written by yamadmin. Posted in How To Articles. The following tips and insights are for your information only. These will not make you an expert tuner. We recommend that if you are a novice, you consult a professional mechanic or technician for your specific needs.

The author cannot be responsible for your interpretation and usage of this information. To visualize how the various circuits overlap, please refer to the jetting chart. Always remember to change one carburetor component at a time and keep a record of your changes.

Depending on your type of riding, adjust the minimum idle speed to desired RPM making sure the engine is up to operating temperature. If you do not desire any idle, make sure you turn in the adjusting screw just enough so the engine will not idle. This is especially important on Keihin PJ Series carbs in that the idle adjust knob 4 in illustration cannot be completely closed.

Such an adjustment will result in a sluggish response off idle. The carburetor pictured in the exploded view uses an air adjustment screw 5 in illustration that is located "upstream" of the throttle valve slide and meters air. Turning the air screw counter-clockwise leans the mixture off idle. Some carburetors have this screw located "downstream" of the throttle valve, in which case, the screw meters fuel and opening the screw counter-clockwise results in a richer mixture.

The idle screw usually has a range of one to two turns out from fully closed. Consult your owner's manual for the standard setting.

The slow jet calibrates the mixture from both the idle bypass and the idle orifice in the jet block. Consequently, if the throttle is only partially opened, such as in a trailing throttle situation, and the bike tends to load up, emitting a deep tone when the throttle is returned to full open, it is usually a sign of a rich slow jet. If the slow jet does not clean up this part of the circuit, the slide can be substituted for one with a different cutaway.

How it overlaps with the jet needle depends on the jet orifice inner diameter, air bleed holes and type of nozzle screen. MAIN JET: The best track side method to determine the size of the main jet 7 in illustration is to fully load the engine on a long straightaway or hill.

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At the end of the stretch, chop the throttle and hit the kill button simultaneously. Now pull the spark plug. Best power will usually result in a very light tan colored insulator tip and dark colored ring around the tip of the electrode. The electrode itself should have fairly sharp edges. For example, if the ceramic insulator has a nice tan coloring but the electrode has a white ring around the tip and the plug is of the correct heat range, then you can easily run a size larger on the main jet.

When jetting your main jet, try to remember to jet for the best power in a specific situation. As you gain experience and knowledge, you will be able to use other methods to determine your jetting. A good tuner can "feel" most of the circuits by slowly reving a parked bike, or just by looking at the color of the unpainted pipe and silencer.

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Rejetting the Carburetor on a Harley Twin Cam

Mobile Login Quick Registration.Fuel mileage 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.

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The speed at which you travel is one. When I talk with someone about fuel mileage, I find it useful to set a test standard. These are conditions most of us can find and safely use. Using this standard, stock Harleys "drar normalt 0. 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 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 0.

The big touring machines usually get closer to 32 0. 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 mpg bike will probably start misfiring due to its over-rich condition by 4, feet, maybe even 3, By contrast a stock or correctly jetted engine should get to at least 6, feet before getting grossly rich, 7, feet is better and achievable.

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This is also true of all road-going bikes sold in America for the last quarter century. And therefore, it shares similar parts which perform similar functions. Both the jet size and screw setting are important. 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. One normally raises or lowers the needle to fine-tune mixtures within this range. 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.

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. Get your stock carb right l.Harley-Davidson Motor Co. Since then, all Harley-Davidson motorcycles make use of fuel injection. The CV carburetor may show signs of needing to be tuned. These signs include a drastic decrease in fuel economy, black smoke appearing from the exhaust, sluggish acceleration, the engine spitting back through the carburetor, or hesitating upon acceleration.

A low-speed circuit adjustment to the carburetor can be made in minimal time. Check spark plug for light-brown glassy deposits which may be accompanied by cracks in the insulator or erosion of the electrode, which indicates a lean air-fuel mixture. Dry, fluffy or sooty black deposits indicate a rich carburetor air-fuel mixture.

harley cv carb jetting chart

Locate the idle mixture screw on the bottom outlet side of the carburetor, in a passageway next to the float bowl. Turning the idle mixture screw in, or clockwise, will lean the idle mixture and turning it out, or counterclockwise, will enrich it.

Drill out the metal plug covering the idle mixture screw. Do not drill too far into the plug; wrap the drill bit with tape or string to prevent you from drilling too far and damaging the screw.

Turn the idle mixture screw in clockwise until it stops. Do not over-tighten the idle mixture screw. Damage to the screw and its seat may result.

Turn idle mixture screw two turns out counterclockwise to an idle speed of 1, rpm. After each adjustment, reset the idle speed to 1, rpm. This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.

To submit your questions or ideas, or to simply learn more about It Still Runs, contact us. Step 1 Check spark plug for light-brown glassy deposits which may be accompanied by cracks in the insulator or erosion of the electrode, which indicates a lean air-fuel mixture. Step 2 Locate the idle mixture screw on the bottom outlet side of the carburetor, in a passageway next to the float bowl. Step 3 Drill out the metal plug covering the idle mixture screw. Step 4 Pry out the plug with a small pick.

Step 5 Turn the idle mixture screw in clockwise until it stops. Step 6 Turn idle mixture screw two turns out counterclockwise to an idle speed of 1, rpm. Tip When adjusting the idle mixture screw, make only small adjustments. Often the smallest adjustment is all that is needed. Warning These procedures may reduce or void any limited warranty coverage.

About the Author This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. Photo Credits moteur image by Jerome Dancette from Fotolia.Subscribe today to get your hands on all our DIY tech stories every two months for less than half the cost of the cover price. All modern Harleys are fuel-injected, but not so long ago Harleys came fitted with a CV carburetor, the best carb H-D would ever put on its bikes.

Though some owners would swap them out, the CV, with the proper jetting, can handle most moderate performance modifications. That is, if you know what to do and what size jet to install, which brings us to the reason for this article. When the mixture is too lean, the engine will take forever to warm up, cough out of the carb when you try to accelerate, surge when you try to hold a steady speed, and ping like hell on a hot day detonationjust to name a few problems.

And if you have to hold the throttle open to keep the engine running while you watch the header pipes turn red where they attach to the heads, the engine is way too lean! As surprising as it may be for some owners, an air cleaner or exhaust change will usually lean out the mixture.

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A ratio of about These numbers represent the ratio of air to fuel in the mixture. The larger the number, the bigger the hole in the center of the jet, so more fuel is added to the air coming through the carb.

For example, a 40 slow jet has a. A 45 slow jet has a. However, if you made a big alteration to the engine, like punching an Sportster out to cc, make the first main jet change two sizes larger richer. Then, if needed, richen or lean out the jetting one jet size at a time until the engine runs correctly.

This is safer than running the engine very lean during the jetting tests after a major engine alteration and causing detonation, overheating, and possible engine damage. Rejetting a CV Carb. American Iron March 15, Previous Article. Next Article. Recent Posts. Indian Announces Launch of Click.


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