On a manual transmission car the idle speed adjustment can be set with the transmission shifted into neutral and the parking brake is set. If your aftermarket holley is equipped with four corner idle circuits such as the 4781 shown in the photo set the front first then set the rear.
Holley Fast Idle Cam Red
Holley fast idle adjustment. Use an open end 14 wrench and using the mirror place the wrench over the screw. For the initial adjustment all idle screws should be within 14 turn of each other although you may have to turn the primary screws out an additional 18 to 14 turn. Then rotate it back slowly until the choke plate just comes closed. Recheck the front idle after the rear setting has been confirmed. Slightly crack the throttle open unload the fast idle cam and turn the choke cap clockwise until you see the choke plate open. This will drop a lever under the choke housing with a 14 screw in it to slow it down.
Turn it clockwise to speed it up turn it counter clockwise to slow it down. Move the wrench toward the rear of the car to reduce the fast idle toward the front of the car to increase the fast idle. Reduce the engine idle speed and repeat the process until the engine idles at the desired rpm. Step 6 adjust all of the idle mixture screws by turning them clockwise and counter clockwise until the vacuum gauge reads the highest possible vacuum reading. Recheck the front idle mixture after the rear setting has been set. Reduce the idle speed and repeat the process perhaps several times until the engine idles at the desired engine speed.
Turning the screw clockwise will. Nothing else fits with the mirror in place. At that point you can go ahead and snug those screws back up and thats going to give you a good starting point to make adjustments from. First find your idle rpm setting from under your hood or from a repair manual. Rest a mirror on the manifold pointed upward so you can see the fast idle adjustment screw. Here we show you how to properly adjust the curb idle speed on your holley carb.
To adjust the fast idle you will need to hold the throttle wide open without the engine running.
Gallery of Holley Fast Idle Adjustment
