First of all, I think this entire thread should be in the "other bikes" section, instead of the SOHC4 technical forum.
I request that the moderator move it to there.
Assuming your 350 twin carbs work in the same way the SOHC4 carbs do, then the air screw only effects the first 1/4 or less of the throttle travel and corresponding engine RPM.
Raising the float level does have a richening effect across the entire throttle range. But, I speculate that will not be enough to compensate properly for lack of air filter restriction.
More likely, the slow jet, throttle valve needle/jet, and main jet will need to be changed to allow more fuel to be drawn through the carburettors.
Best of luck!