Next is setting up the idle. If your Corvette has a big duration camshaft (and a very lumpy idle), you'll find the idle mixture screws tend to be unresponsive. There's an easy fix: Adjust the secondary throttle stop screw. Holley four barrels have a small setscrew located beside the passenger-side throttle-bore shaft bore (on the base plate of the carburetor). By turning the screw clockwise approximately 11/2 turns, the throttle blade on the secondary will open slightly. This results in a rather large amount of airflow through the carburetor, without increasing the "window" seen by the idle transfer slot. At this time, the primary throttle blades can be closed, which tends to enhance the sensitivity of the idle mixture control.