carb choice and slick size

Carter's have mechanical operating secondary butterflies that have a velocity air door above it loaded on a spring. When this air valve is overcome by demand it will open. It is not a vacuum sensitive item by a air velocity issue. AKA, air demand for the engine.

The spring on the secondary side is an easy adjust for sooner or later openings with 2 screwdrivers. The AFB is a counter weighted air door that is not easy to readjust. Sometimes the quick opening of the valve will cause a flat spot. Mods can fix this though it is a pain to do and expensive if you screw it up or have it done for you.