How to Adjust the Air-Fuel Mixture on a Motorcycle Carburetor?

[VonGia]

First, adjust the idle screw to the highest possible setting, then adjust the mixture screw towards the lean direction, or in the direction that reduces the idle speed. Check if the spark plug is prone to carbon buildup. If there is carbon buildup, adjust the mixture and idle speed according to the above method.

[LeKeira]

I've been studying how to adjust the motorcycle carburetor mixture ratio for years, and it basically comes down to four steps: First, warm up the engine for five to ten minutes to get it in the right state—you should feel heat when you put your hand near the exhaust pipe. Next, locate the small screw on the side of the carburetor, usually near the throttle valve, and gently turn it with a flathead screwdriver—clockwise to lean the mixture, counterclockwise to enrich it. The key is to listen to the engine sound and stop when the RPM reaches its steadiest point, then fine-tune it back by an eighth of a turn. Finally, don't forget to adjust the idle screw to bring the RPM back to around 1000. When test-riding, if the acceleration feels smooth without hesitation, you've got it right. Bringing a temperature gun can help prevent burns from over-adjusting—this skill improves with practice.