How to Clean a Carburetor

To learn how to clean a carburetor, you want to start by getting an air compressor, an air gun and two cans of carburetor cleaner.

There are two distinct styles of carburetors, the internal float as in Rochester Quadrajet, Thermoquad, Carter AFB and the Edlebrook; then there is the exterior mounted dual float carburetor such as the Holley. The principles of cleaning the carburetors remain the same even though the procedure differs.

Internal Float Carburetors

Place a clean cloth on a flat surface to lay the parts and keep them in order. Remove the top of the carburetor with a Phillips screwdriver. Be careful not to damage the underlying gasket. Once the screws are loose lift the top slightly and angle it to release the choke rod from the choke plate. Remove the top carefully because the main metering rods are attached to the top. Do not drop or damage them in any way. Lay the top on the cloth.
Remove the float and needle by lifting the float rod out of its cradle. Do not lose the needle and the tiny spring attached to it.

Remove the two idle mixture screws located in the front bottom of the carburetor along with the tension springs. Use a common screwdriver to remove the main jets on the bottom of the float bowl. Put the plastic tube on the carburetor cleaner and spray it into each of the two vacant idle mixture screw holes. When they are clean and clear, a stream should appear under the throttle plate in the bore.

Clean the two main metering jet holes in the same fashion. A jet of cleaner should appear out of the tubes that extend out from the upper portion of the bore just under the choke plate. Clean the jets also. Clean the hole in the bottom of the accelerator pump well located in the float bowl. Clean the needle and seat from which the needle and float were taken. Clean the interior bore and all holes in the housing to include the vacuum ports.

Use compressed air and the air gun to thoroughly blow all the holes out. Reassemble the carburetor in reverse order of removal. Keep in mind to carefully install the top by lining the two main metering rods up with the main jets in the bottom of the float bowl. Do not force the top down. If the metering rods are lined up in the holes the top will go on easy. When installing the idle mixture screws, turn them in all the way but do not tighten them at all. Turn them back out 2½ turns.

Holley Carburetors

Use a common screwdriver and a 5/8-inch wrench to remove the needle and seat in the front and rear float bowl by removing the top locking screw followed by turning the underlying nut counter-clockwise to remove the needle and seats. Remove the four bolts securing each float bowl to the main body. Remove the bowl and lift out the float mechanism by its rod.

Remove the accelerator pumps by removing the four screws in each pump located under each float bowl. Unscrew the two main metering jets on both sides of the carburetor that are screwed into the metering body, but do not remove the metering body. Keep these jets separate, since they are of two different sizes and they will not work if they are interchanged. Remove the idle mixture screws--one on each side of the metering body. Be careful not to lose the tiny felt o-ring on the needle.

Clean all passages made vacant by the removal of these parts. Use carburetor cleaner to clean them, then blow out all the ports and passages made vacant by the removal of the parts.

Install all the parts in reverse order of removal. Adjust the idle mixture screws all the way in and turn them back out 1¼ turn. Holley carburetors are the easiest to clean and have the least amount of moving parts. When the engine is started, allow it to reach normal operating temperature, then set the mixture and idle accordingly. 

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