Quadrajet Tuning Tips

Air door adjustment:

To adjust the air door tension use a small flat head screwdriver and an allen wrench. Loosen the allen screw first to unlock the adjustment screw. The tension is adjusted using the flat head screwdriver. Once desired tension is obtained lock the screw in place by tightening the allen screw.












APT (Adjustable Part Throttle) adjustment:

Use a 3/16 allen wrench to remove the 3/16 set plug shown in the photo to access the APT adjustment screw beneath it. Using a small phillips head screwdriver turn the screw clockwise for a leaner mixture, counter clockwise for a richer mixture.






Curb idle adjustment:

The curb idle screw adjusts the idle speed when the vehicle is warmed up and the choke is off. Use a flat head screwdriver to adjust the curb idle speed screw shown in photo. Turn the screw clockwise for a higher idle speed, counter clockwise for a lower idle speed.








Fast idle screw adjustment:

The fast idle screw adjusts the idle speed when the vehicle is cold started and the choke is on. Use a flat head screwdriver to adjust the fast idle speed screw shown in photo. Turn the screw clockwise for a higher idle speed, counter clockwise for a lower idle speed.












Idle fuel mixture screw
adjustment:

There are 2 types of idle fuel mixture screws, the one shown in the photo on the right is external to the base and is adjusted with a flat head screwdriver. The other type is embedded in the base and is shown below. Both types are adjusted the same. Turn the screw clockwise for a leaner mixture, counter clockwise for a richer mixture.






The imbedded idle fuel mixture screw is adjusted using either a 3/16 hex socket or a GM Double D adjustment tool. Turn the screw clockwise for a leaner mixture, counter clockwise for a richer mixture.