Mike,
The Holley info in post #9 is correct. Holley knows how their carbs work.....& other venturi carbs work the same way. With no air flow through the venturiis, the fuel in the main well is the same as the fuel level in the float bowl [ actually, slightly lower because the idle fuel is drawn from the main well ]. If you look at the sight plugs in the fuel bowl, you will see that the fuel level [ bottom of the the threads ] is about 1/4-3/8"
lower than the booster entrance on the main body [ this is called the spill height ].
The fuel in the well has to be lifted before it can enter the booster. The air bleed [ AB ] bleeds off some of the depression at the booster, where the suction [ vacuum ] is being applied. The depression/suction is created by the air flow past the booster. With a bigger AB, more suction is lost & more air speed [ rpm ] is reqd to build up enough suction to initiate flow. Small AB starts the main system earlier, & vice versa.
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