The Holley 600 is a large displacement carburetor, rated at 600 cubic feet per minute of air flow. This carburetor is designed for use on large plenum intakes and large displacement engines alike. Adjusting the 600 will be done with the carburetor installed on the engine and include adjustment of the fuel float level and the idle mixture screws. The fuel float regulates the amount of fuel stored in the carburetor at any given moment, and the idle mixture screw controls the release of that fuel to ensure idle and acceleration are smooth and crisp.
Park the car on a level surface, unscrew the air filter wing nut and pull off the air filter cover, filter and filter base.
Unscrew the fuel level sight plug and rock the car side to side, looking for a slight trickle of fuel to come out of the sight hole. If no fuel comes out, the float need to be adjusted up. If fuel pours out, the float needs to be lowered.
Unscrew the float adjustment screw two turns and pry the adjustment nut slightly upwards to break the adjustment assembly's seat on the bowl. With the engine running, watch the sight hole and adjust the float nut clockwise to lower or counterclockwise to raise the float until fuel trickles out of the sight port.
Tighten the adjustment screw while holding the adjustment nut stationary with a wrench.
Reinsert the fuel level sight port screw and tighten. The fuel level is adjusted.
Locate the idle mixture screws, one on each side of the metering block. The metering block is the section of carburetor between the fuel bowl and the choke tower (main body of the carburetor where the air filter sits).
Screw both screws clockwise until they "bottom out" and back them out exactly 1 1/2 turns. With this as a common starting point, start the engine.
Adjust each screw equally, in increments of one-half turn until the recommended rpm idle range is reached, as per your engine's service manual.
