Jetting Keihin CV Carbs

We got a 1996 XL883 Sporty in this week for some carburetor issues. It had a 48 slow jet and a 190 main jet on an otherwise stock bike. Holy Moly! BIGGER IS NOT ALWAYS BETTER.
Here are a few tips for jetting Keihin CV carbs.

1. Eliminate intake air leaks. If you are fighting an intake leak you are already losing the battle. With the bike running, spray a little shot of brake cleaner from an aerosol can with a long straw on the intake flanges where they meet the heads. If the bike bogs out you have an intake leak. Replace the seals.

2. Make sure you are using good, fresh fuel. Check the fuel tank for rust in the bottom and on the petcock screen. Debris in the float bowl can plug up jets and interfere with normal float operation.

3. Clean the carb and inspect all the components. Spraying "carb cleaner" in the intake is NOT a substitute for a carb bath and new seals and orings. The vacuum piston can get burnt and worn over time also. Replace any damaged or worn parts and all seals before any tune.

4. Use the proper tools. Carb screws are notoriously easy to strip and round out. Also a good punch set is recommended. You don't want to replace a expensive carb body because you broke it with a hammer or broke a mixture screw off.

5. Know what you are working with. Engine mods play a vital role in jetting. But also knowing whats in your carb will help you out. Unfortunately there are a many different aftermarket "Stage" kits available for carbs. Knowing which kit you are working with will help you tune. We use and recommend the DynoJet kits.

6. READ THE DIRECTIONS!!! All the older Harley-Davidson Service Manuals have extensive carburetor tuning sections. Also all of the DynoJet kits come with detailed instructions. These will tell you exactly what jets to install, where to put needle settings and how to set floats and mixture screws. They also offer guidance on troubleshooting for problems. Incidentally most of the instructions are readily available online.

7. Don't modify components. There is no reason to go with the "poor man's jet kit." Don't cut loops out of springs to make them softer. Don't drill out jets to make them bigger. These parts are inexpensive and readily available. There is no need to butcher them for a proper tune. Only modify parts if your instructions tell you. (i.e. Drill out vacuum piston air hole)

8. In conclusion, armed with good, clean components, the proper tools, the right information and a little patience. You should be able to achieve a streetable and rideable tune for any Harley-Davidson Air Cooled V-Twin running a CV Carburetor without having to put it on a dyno.

 

 Don't do this.  Wrong hardware.  Wrong Air Cleaner for Carb.  Mounted with out a support bracket to attach to the heads.  This actually covers up vacuum holes that need to be there for carb to work properly.