The Holley two-barrel carburettor is designed with two adjustment screws located near the base of the carburettor. 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 carburettor can be done in just a few minutes. You can adjust the carburettor 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 carburettor. Turn the screws carefully with a screwdriver in a counter-clockwise direction, until the screws bottom out and you feel resistance.
Turn both screws clockwise 1 1/4 turns to use as a starting point to adjust the carburettor. Start the motor, letting it warm up for about five minutes.
Remove the rubber vacuum hose from the vacuum port on the side of the carburettor. Attach a vacuum gauge to the vacuum port.
Adjust the screws, moving them 1/8 of a turn at a time in a clockwise direction, alternating back and forth. Continue adjusting until both screws have readings of 600 RPMs on the vacuum gauge.
Remove the vacuum gauge from the vacuum port on the carburettor, by hand. Attach the vacuum hose to the vacuum port.
Shut the engine off and allow it to cool down.
Always be cautious not to get burnt by hot engine parts when adjusting the Holley two-barrel carburettor.