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Guide to Motorcycle Carb Tuning, Adjustment and Jetting

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Clean, smooth acceleration happens when all components of the carburetor are clean and tuned properly. The right sized jets, needle positions, and float settings will ensure there is no fumbling or flat spots from idle all the way to wide open throttle.

Troubleshooting Motorcycle Carbs

If your motorcycle engine doesn’t seem to be running correctly, it’s probably either too rich or too lean.

Learn more about general symptoms of running lean vs rich.

Rich or lean running conditions can be caused by any number of things, so you’ll need to first clean, sync, set and balance your carbs before making too many changes.

How to Adjust Air Fuel Mixture at Different Throttle Positions on a Motorcycle

If you remember what throttle position each component of the carb control, you can begin to make some adjustments depending on the running conditions you experience.

Adjusting from Idle to 1/4 throttle range

  • Turn the air screw in to richen the mixture.
  • Back the air screw out to lean the mixture.

If your airscrew is on airbox side of carb, turning out will lean mixture. If airscrew is on engine side of carb, it will richen it. 

Adjusting from 1/4 to 3/4 throttle range

  • Raise the needle jet clip to lean the mixture.
  • Lower the needle jet clip position to richen the mixture.

Adjusting 3/4 to wide open throttle range

  • Use a larger main jet to richen the mixture.
  • Use a smaller main jet to lean it out.

Effects of Air Temperature, Altitude, and Humidity Conditions on the Air/Fuel Mixture

High air temperature, high altitude, and high humidity conditions require a leaner mixture.

Low air temperature, low altitude, and low humidity conditions require a richer mixture.

More Resources for Tuning your Motorcycle Carbs