Adjusting a Holley carburetor is a job that can be done in just a few minutes. Occasionally, the adjustment screws on a Holley carburetor will loosen from engine vibration while it is running, causing the motor to run poorly and reducing your fuel mileage. A poor running engine can also cause engine parts to fail quicker. You can adjust the Holley carburetor yourself, saving you the time and money of having a mechanic or someone else do the work for you.
Locate the two idle mixture screws on both sides of the Holley carburetor metering block between the body of the carburetor and the float bowl on the side.
Turn the adjustment screws gently with a screwdriver while the engine is off, turning the screws counter-clockwise until they bottom out. Turn the screws until you feel just a slight resistance to keep from over-tightening them.
Rotate both screws clockwise 1-1/4 turns with a screwdriver to begin the idle adjustment. Turn the motor on and let it warm up for about five minutes.
Pull the vacuum hose off the vacuum port at the bottom of the carburetor and attach a vacuum gauge to the vacuum port.
Turn the idle adjustment screws on the Holley carburetor 1/4-turn clockwise at a time until the RPMs on the vacuum gauge reach 600 for both adjustment screws.
Remove the vacuum gauge from the vacuum port and reattach the hose to the port. Shut the engine off.
