Holley makes a number of different models of carburetor, including the Rochester 2G. After cleaning the carburetor or rebuilding it, the idle mixture, which controls the amount of fuel that flows into the carburetor, must be adjusted. A richer or greater amount of fuel requires less vacuum to move through the carburetor, which is important if driving at a high altitude. Lower altitudes require a leaner mixture or less fuel.
Locate the idle mixture screw on the Rochester 2G carburetor. It will be on the passenger side of the carburetor, just ahead of the choke hosing and beneath the small brass vacuum tube, which is not connected to a hose. The idle mixture screw is covered with a plastic cap with a "X" printed on it.
Remove the plug covering the idle mixture screw by prying it out using a flat head screwdriver. The screw head of the needle control will be revealed.
Start the engine and let it warm up to normal operating temperature.
Adjust the idle mixture to the desired lean or rich fuel mix. Turn the screw head in counterclockwise to make the mix richer or, turn the screw out clockwise to make it leaner.
