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Step #1 in the process is filling the carburetor's fuel bowls with fuel. If you're running a mechanical fuel pump, disconnect the coil wire and crank the engine over for about 10 seconds to allow the fuel bowls to fill. This procedure will help prevent any back fires. Reconnect the coil wire when finished.

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.

One of the most crucial, yet overlooked adjustments in a Holley four-barrel carburetor is the float. Adjusting the float and fuel level on a Holley four-barrel carburetor is easy if you follow a few basic steps.

But it’s important to know how the fuel float system operates first.

float-5The floats, located in the fuel bowls of Holley four-barrel carburetors, control the fuel delivery system and ensure that the carburetor has a sufficient fuel supply. Some of the most common symptoms of improperly adjusted or sticky floats are hesitation on acceleration, a rough idle, flooding and misfires. Obviously, making precise fuel float, and in turn, fuel level adjustments is difficult on a misfiring or rough idling engine.

So the procedure to adjust this has to begin without the engine running.

Scroll the slideshow above to learn the basic steps for adjusting the fuel level and floats on a Holley four-barrel carb.

All images/Dan Sanchez and Holley

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Author: Dan Sanchez

Dan Sanchez is the president at DS Media, an agency that specializes in content marketing and online advertising and PR strategies. Sanchez is also an author, editor, and regularly contributes to a number of automotive enthusiast and B2B publications.