How to Adjust the Fuel Level and Floats on a Holley Four-Barrel Carburetor

If you're using an electric fuel pump, let the fuel bowls fill in stages by turning the ignition key on and off, only letting the fuel pump run a few seconds at a time. This will help prevent the needle from seating improperly.

Next, you'll need to check the fuel pressure. Attach a fuel pressure gauge and check the fuel pressure. Flooding will happen when pressure exceeds 7.5 psi. According to Holley fuel techs, the fuel pressure should be no more than 7 psi; 6 psi is ideal.

Use the carburetor's sight plugs to inspect the fuel level. With the engine off, remove the sight plugs from the fuel bowl to check the current fuel level. With the proper fuel pressure and float level setting, a slight trickle of fuel should be seen at the bottom of the sight plug hole when the vehicle is gently rocked in a side to side motion. If no fuel is seen at the plug hole, the fuel level is too low. If fuel flows freely from the sight plug hole, then the fuel level is too high. Anything other than trickle from the bottom of sight plug hole will require extra adjustment of the float to correct the fuel level in the bowl.

If you didn't see any fuel trickle out of the sight plug, the float is not allowing enough fuel to get into the fuel bowl.

With the engine off, raise the float assembly in the fuel bowl by loosening the lock screw on top of the fuel bowl. Make only a few turns and then gently pry up on the adjusting nut underneath to break the seal on the gasket. Cinch the locking screw down tight again before starting the vehicle. Start the engine and remove the sight plug.

Turn the lock screw counter clockwise with a 5/8-inch box wrench to loosen. (Vehicles with electric fuel pumps do not need to be started for fuel level adjustment.) Wear safety glasses and cover the needle with a rag during the adjustment. The fuel will be under pressure and will most likely discharge at the needle when performing a float level adjustment on a running vehicle.

Turn the adjusting nut counter clockwise while holding the lock screw in place up top. This will let the fuel levels rise in the bowl. Keep turning until the fuel level reaches the bottom of the sight hole and starts to trickle out.

If fuel is pouring out of the sight plug then the fuel level is set too high, and the float must be lowered in the fuel bowl.

Loosen the lock screw, and turn the adjustment nut clockwise for about 1/2 to 3/4 of a turn and then retighten the lock screw. Start the engine to refill the fuel bowl and check to see the where the fuel level is in relation to the sight hole. Continue the proper procedures until the fuel level is at the bottom of the sight hole.

When the level looks correct, reinstall the sight plug and tighten it. On Holley models with sight windows, the fuel level should just appear in the bottom of the window. Once you've made all your adjustments to the fuel float, make sure to tighten the locking screw while holding the adjusting nut with the box-end wrench.