Adjusting the Aperture on a Quadrajet Carb

Adjusting your Quadrajet's aperture can boost its efficiency significantly.

A Quadrajet carburetor has four barrels, but the barrels are not of equal size — the "primary" ones are significantly smaller than the "secondary" ones. A piston manages the air-to-fuel ratio by shifting the metering rods, and the aperture through which air enters the carburetor is a key element in overall efficiency. When you tune a Quadrajet carburetor, you adjust the size of this aperture.

Things You'll Need

• Auxiliary tachometer
• Screwdriver

Instructions

1. Look at the side of each barrel on the Quadrajet carburetor. You'll find a pair of adjustment screws; tighten them until you can feel them contact the bottom of the fitting. Then turn counterclockwise three rotations.

2. Start the engine and have it idle until the temperature gauge shows its normal operating level. Then unhook the vacuum hose from the Quadrajet and attach it to your auxiliary tachometer.

3. Tweak the settings of each screw until you maximize each screw's reading on your tachometer. Then adjust the screws until idling shows an RPM around 1,000.

References

• The Carburetor Doctor: Carburetor Technical Information
• Fateback: Rochester Quadrajet Carburetor Guide
• Underhood Service; Diagnostic Dilemmas: Servicing Quadrajet Carburetors; Gary Goms; May, 2008.