at what point does 6 pack dump fuel?

i'm kind of working on my 6 pack.

at first the idol was too high. i figured out the linkage was binding and screwed them into the correct position. the 2 outside carbs were dumping fuel.

but I'm wondering at what point do the 2 outer carbs actuate? I'm guessing at wot. But I dont see anything physical that controls the levers.