The air/fuel mixture screw is normally plugged off at the factory to prevent for tampering. You won't even find it in a Harley parts catalog. These ones fit the Keihin CV carburetor on all 1988-2006 Sportster, all 1990-1999 Evolution Big Twin, 1999-2006 Twin Cam and 1992-2006 Buell. Come complete with o-ring, spring, washer and thumb screw for easy adjustment.