Properly adjusting a Holley carburetor’s air/fuel mixture is one of the most commonly overlooked and important considerations. A mixture which is too rich, meaning the mixture does not have the proper quantity of air, can result in fouled sparkplugs and poor gas mileage. If the mixture is too lean, meaning that the mixture has too much air, the mixture can actually destroy the engine if left uncorrected. Thankfully, adjusting the mixture on a Holley carburetor is quite simple, as the mixture screws are located on the outside of the carburetor and can be quickly adjusted with a screwdriver.
Locate the two air/fuel mixture screws on the metering blocks. Holley carburetors consist of a “body” and several components which attach to the body. The “body” of the carburetor is the large, square-shaped center section of the carburetor. At both the front and back of the body is a single float bowl.