How to Tune a Holley 750 Carburetor

The Holley 750 carburetor needs to be tuned periodically to maintain maximum performance levels.

Carburetors were used in engines until the 1990s as a way to control the air and fuel mixture needed to operate a vehicle. They were later replaced by fuel injection systems, which provide better control, lower emissions and higher gas mileage. Carburetors are not completely extinct, however. They are still used in car restorations and high performance engines, such as those used for racing.The Holley 750 carburetor is a double pumper carburetor used for high performance engines. It utilizes two manually-operated accelerator pumps and a cable-controlled choke that can be operated from the vehicle's interior.

Things You'll Need

• Large, flat head screwdriver
• 5/8-inch wrench
• 3/8-inch wrench
• Air cleaner gasket

Instructions

Fuel Level

1. Remove the air filter from the engine. Start the engine and allow it to idle until it reaches operating temperature. Shut the engine off.

2. Use a large, flat head screwdriver to remove the fuel sight plugs on the float bowls.

3. Adjust the fuel level by adjusting the float until fuel can be seen through the bottom. Set the floats by holding the nuts on top of the float bowl with a 5/8-inch wrench and loosening the screw on top of the bolt. Turn the nut clockwise to raise the fuel level; turn it counterclockwise to lower the fuel level until it is at the correct level.

4. Tighten the top screw when the correct fuel level is achieved.

Accelerator Pumps

1. Adjust the rod on the accelerator pump.

2. Locate the throttle linkage bolt head on the arm of the accelerator pump.

3. Use a 3/8-inch wrench to adjust the bolt head on the throttle linkage. The slightest movement of the throttle lever should move the accelerator pump lever. This is done by tightening and relaxing the pump override spring.

4. Repeat these steps with the second accelerator pump.

Idle

1. Start the vehicle and check that there are no leaks in the fuel line or inlet fittings. Check that all vacuum hoses are properly secured.

2. Adjust the idle with the idle mixture screws located on the throttle linkage. Increase the idle by turning the screw clockwise; decrease the idle by turning the screw counterclockwise.

3. Position the air cleaner gasket onto the carburetor air cleaner sealing flange. Install the air cleaner.

Tips & Warnings

• To achieve the best idle setting, turn the needle 1-1/2 turns from the full lean position and turn clockwise or counterclockwise to adjust.

• The air cleaner and throttle lever need adequate clearance to prevent uncontrolled engine speed.

References

• Holley: Performance Carburetor Installation and Adjustment Instructions (PDF)
• Bob 2000: How to Tune Your Holley Carburetor

Resources

• Holley