what does a fuel screw do?

[400EXracer74]

what exactly does the fuel screw do?

[Goose19561]

Try this link. Motorcycle Carburetor Theory 101

http://www.motocross.com/motoprof/moto/mcycle/carb101/carb101.html

[04'400ex'er]

It adjusts the mixture of the air and the fuel. It is connected to the pilot jet. It can be backed out to richen the mixture or screwed in to lean out the mixture.

[cals400ex]

i find it to mainly control the air-fuel ratio from idle to 1/8 throttle or less. if the bike is running rich at idle, turn the screw in. if it is running lean, turn the screw out. it is mainly a fine tune adjustment for the pilot jet (slow jet).