It seems like the throttle butterflies are not sync'd but difficult to be realized as 1 & 2 as well as 4 & 5 are on a common shaft, typically #3 is out of whack with 1 & 2 and # 6 is similarly out of whack with 4 & 5.
Pull the carb off, adjust throttle stop screw to be 1 turn from closed (idle position) and look for equivalent light rings around the two butterfly valves in question. They should be pretty close to the same, try it again with butterfly valves fully closed.
Air screws make up for throttle plate timing variations but not larger issues. Also, if the butterflies are not perfectly adjusted in their bores and to each other (throttle shaft twist) your air screw adjustment will only be correct for one idle speed as any change in rotation of the throttle shaft will produce unequal air flows.
I think I'd get them all close as you can and as long as there isn't any spitting and the car runs well then call it close enough.
Paul Abbott
Performance Oriented