Holley Carb problem

That could also (and more likely) indicate not enough initial timing, so the idle speed screw is turned in too far causing it to idle on the main metering circuit. You can verify this by looking down the throat of the carb while it is idling. If you see fuel being pulled through the Venturi's it is idling on the main circuit.

Increasing the initial timing speeds the engine up, you can then turn the idle speed screw out to slow it down and it will start idling on the idle circuit. Once this happens your idle mixture screws will be effective.