How to Set a Float Level on a Holley Carburetor

by Kelvin Hayes

The floats on a Holley carburetor control fuel delivery by regulating the amount of fuel the pump can bring into the carburetor. If the float valve is set too low, known as running "lean," the carburetor and engine will be starved for fuel and run hotter. If the float valve is set too high, the carburetor will become flooded, causing a "rich" air fuel mixture that may foul the spark plugs with unburned fuel. The float adjustment will help avoid a lean or rich mixture and can be performed with the carburetor attached to the engine.

Remove the main coil wire, if your engine uses a mechanical fuel pump, and turn the engine over for approximately ten seconds to fill the fuel bowls. Reconnect the coil wire when finished. For electric fuel pumps, turn the ignition on and off three to five times at 3-second intervals to fill the bowls. There is no need to start a vehicle equipped with an electronic fuel pump.

Locate and remove the fuel bowl sight plugs found on the side of the fuel bowl, using a flat head screwdriver. Rock the car gently side to side while watching for a slight trickle of fuel from the sight hole. If no fuel comes out, the fuel level is too low and would indicate the float needs to be raised. If fuel pours out of the sight hole, this indicates that there is too much fuel in the bowl and that the float will need to be lowered.

Reinstall the sight plug screw.

Loosen the lock screw on the top of the fuel bowl slightly and pry up on the adjusting nut under the lock screw. This is to be done with the engine off, and will serve to free up the adjusting nut from the lock screw gasket -- avoiding a gasket tear during the lock screw adjustment.

Retighten the lock screw and start the engine. Note that vehicles with electronic fuel pumps don't need to be started at all during this process. They require the ignition to be turned on instead.

Remove the sight plug screw and turn the float valve locking screw counterclockwise.

Hold the locking screw stationary with a screw driver while rotating the adjustment nut with a box wrench. Clockwise rotation of the adjustment nut will lower the float, restricting fuel flow. Rotating counterclockwise will create the opposite effect. Note that because the fuel is under pressure, some fuel discharge will occur around the locking nut assembly.

Watch the bottom of the sight hole as you make your adjustments. Once a slight trickle out of the sight hole is achieved, you've set the fuel float valve at the correct level. If the fuel level is too high, turn the engine off, and rock the car side-to-side with the sight plug open. Once the bowl is drained, turn the adjustment nut clockwise, lowering the float. Start the engine again and make any upward adjustments to the float until a slight trickle on the sight plug is achieved.

Reinstall the sight plug screw.

Tighten the lock screw while holding the adjustment nut in place with a box wrench.

Items you will need

About the Author

Kelvin Hayes has been writing professionally since 2009 as a freelance copywriter. He runs his own online business, writing ebooks, reports and information products. Completely self-taught, Hayes prides himself on creatively completing writing projects by pulling from his wide range of life experiences.