How to Adjust a Holley Carburetor

by Don Bowman

Holley carburetors are the most popular and trouble-free variety on the market. Because they consist of few moving parts, wear is not a big factor. Holley carburetors also have the reputation for being the easiest to tune up and offer a wider variety of upgrades to accommodate different displacements than any other carburetor.

Remove the air cleaner. To adjust the choke, move the throttle linkage slightly to the open position and allow it to return. The choke should be closed completely. If it is not, use a Phillips screwdriver to loosen the screws in the black choke-spring housing and rotate it clockwise just until it closes, then tighten the screws.

Start the vehicle and watch for the choke plate to open as the engine warms up. The engine is on fast idle at 1,500 rpm, and the choke begins to open within two minutes. A quick snap of the throttle linkage returns the engine to slow idle. If the choke does not operate, it should be checked for power at the coil spring by using a voltmeter. If there is power, the choke coil is bad.

Shut the engine off. Use a screwdriver to remove the sight plugs located in the float bowls on the passenger side of the carburetor. Fuel should be level with the bottom of the sight plug. If not, adjustments can be made to raise or lower the fuel level with the adjustment nut on top of the float bowl. Loosen the top lock screw with the screwdriver and use the 5/8-inch wrench to turn the nut, which is the adjustment. Turn the nut clockwise to lower the level of fuel or counter-clockwise to raise the fuel level.

Adjust the mixture with the engine running. There are two mixture screws on all 650 CFM and under carburetors and four on larger-bored carburetors. Adjust the screw on the driver's side first, then turn the mixture screw to the right until the engine rpm starts to drop. Stop and turn the screw to the left until the engine reaches the highest rpm, then turn it to the right one-quarter turn. Do the same to the other side, then repeat the procedure one more time.

Adjust the accelerator pump actuating arm by turning the nut at the bottom of the spring where it contacts the throttle linkage. Use a wrench to turn the nut as necessary to make the pump arm on the bottom of the float bowl start to move when the throttle linkage is moved by one-quarter inch.

Items you will need


About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).

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