Wednesday, March 21, 2018

Pilot screw: Tuning the carburetor (Honda Rebel/CMX250C)


Warm engine up thoroughly and set idle at approximately 1400 rpm.

Find the pilot screw. It faces directly downward, located at the bottom of the intake. You will need a very short stubby screw-driver.

Release the tab on the pilot screw that holds it in place. This may be missing due to previous adjustments.

Turn screw either way until the engine stammers, and note the turns.

Turn screw the opposite way until the engine stammers, and note the turns.

Now turn to the point between the two noted turns. 

Clean the area of oil and fix the pilot screw in place. I cannot warrant the following method, however, I applied a small amount of clear silicone paint to keep the pilot screw from moving out of place.


Turn screw in to lean the fuel/air mixture for high altitude (less fuel for a thin air environment). Turn screw out to enrich fuel/air mixture for low altitude (more fuel for the denser air environment) ("air" meaning oxygen).

Honda Rebel Service Manual, section 5-12.

Here is a good review of carburetor operations, however, NOTE, the pilot screw rich/lean directions are opposite the Rebel carburetor:

Disclaimer: I am an amateur posting ideas merely for discussion. Do not implement without confirmation from a professional mechanic. from


  1. Is this process for both single or duel carb? Is not it Would you please inform me how to tune duel carburettor for honda rebel 250 and where is the pilot screw in duel carburettor? is it single or double?

    1. I don't know about duel carb unfortunately.