Does tightening the mixture screw on a motorcycle make it leaner or richer?
1 Answers
Turning it inward makes it leaner, and turning it outward makes it richer. For a 125cc carburetor's mixture screw, turning it inward makes it leaner, and turning it outward makes it richer. For engines below 125cc (excluding scooters), it's the opposite. This is because the 125cc models control fuel quantity, while those below 125cc (excluding scooters) control air. Additional information: For this type of carburetor's mixture screw, turning it clockwise makes it leaner, meaning the more you tighten it inward, the leaner it gets. Turning it counterclockwise makes it richer, meaning the more you loosen it outward, the richer it gets. Only small-displacement bikes like 90cc, 100cc, 110cc, or underbone 125cc carburetors become richer when turned clockwise. Most 125cc slide-type carburetors and almost all diaphragm-type carburetors become leaner when turned clockwise.