Carburetors equipped with adjustable mixture screws allow the tuner to change the amount of fuel delivered to the engine, creating an ideal idle mixture.

Most four-barrel carburetors use two screws to set the idle mixture. Some recent Holley and all Demon carburetors use four idle-mixture adjustment points.

Turn the idle speed screw on each carb all the way out and back in, then 1-1/2 turns from dead-closed. Repeat this step a couple of times as necessary to make sure the screws are in the same ...