On a manual transmission car the idle speed adjustment can be set with the transmission shifted into neutral and the parking brake is set. Turning the screw clockwise will.
Holley 2300c 4160 4160c Carbs
Holley fast idle adjustment. Slightly crack the throttle open unload the fast idle cam and turn the choke cap clockwise until you see the choke plate open. Here we show you how to properly adjust the curb idle speed on your holley carb. Nothing else fits with the mirror in place. 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. Rest a mirror on the manifold pointed upward so you can see the fast idle adjustment screw. To adjust the fast idle you will need to hold the throttle wide open without the engine running.
Reduce the engine idle speed and repeat the process until the engine idles at the desired rpm. Recheck the front idle after the rear setting has been confirmed. 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. Reduce the idle speed and repeat the process perhaps several times until the engine idles at the desired engine speed. Use an open end 14 wrench and using the mirror place the wrench over the screw. This will drop a lever under the choke housing with a 14 screw in it to slow it down.
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. Turn it clockwise to speed it up turn it counter clockwise to slow it down. First find your idle rpm setting from under your hood or from a repair manual. 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. 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.
Recheck the front idle mixture after the rear setting has been set.
Gallery of Holley Fast Idle Adjustment
