The Holley two-barrel carburetor is designed with two adjustment screws located near the base of the carburetor. The curb idle speed screw allows for adjusting the RPMs to the correct level when the vehicle is idling in gear, while the idle mixture screw sets the correct RPM level when the vehicle is idling in park. Adjusting the Holley two-barrel carburetor can be done in just a few minutes. You can adjust the carburetor yourself, thus saving time and money.
Locate the curb idle speed screw and the idle mixture screw; both can be found at the base of the two-barrel Holley carburetor. Turn the screws carefully with a screwdriver in a counter-clockwise direction, until the screws bottom out and you feel resistance.