The air door is spring loaded to be closed. Depending on the amount of load you put on it by twisting the spring tighter or looser will determine when the air door will open.
The air doors opening can be delayed or quickened. The AFB can not easily be adjusted. The difference? If you step on the gas pedal hard to accelerate very quickly, on the engine can tip the AFB’s counter weighted air door open causing the fuel to drop out of suspension. The engine goes lean until the fuel can get into the cylinders to start making power again. On the AVS, the secondary air doors opening is delayed to a point where the engine can consume the added air flow.
Since there is no secondary pump shot of fuel, the engine will see only air from the AFB for a moment. On the AVS, the air door is above the secondary boosters. On opening, the air rushes over the door which directs the air over and into the boosters.
Because the door is delayed in opening, the resulting constant air flow past the boosters and getting fuel moving quicker to the cylinders ends up having a smoother transition and no bog.
IF you have a bog with the AVS carb when getting into the secondaries, the spring needs to be tightened up. As you probably know, it is done on the side of the carb as shown below.
Below is a number of pictures showing various positions of the secondary air door as it opens up so you can see the boosters slowly being uncovered by the air door.
Directly above the boosters, a rectangle slot is cut out in the air door to allow some air to go into and down the booster to Siphon fuel out and get it flowing.
The OE AVS was slightly different in it had no secondary boosters under its secondary air door. Just two tubes with holes drilled into them at various points. The number of holes can vary but I have never seen less than three holes to distribute fuel.
FWIW, Carter rated there AVS carbs at 630 & 750 cfm.
