If you adjust the 'idle screws' out further than 2 turns, there is no further mixture change. The operating range of the idle-mix screws is 1/2 to 1-1/2 turns, with only a 3%-4% increase out beyond 1-1/2 turn, which is wide open at 1-3/4 turn.
The mixture gets richer as the screws are turned outward.
If it won't idle or run correctly at 1.0 turn out, + or -1/4 turn either way from there, then something is amiss elsewhere and needs to be found. With the 064a carbs I'd suggest looking at the holes in the emulsifiers, make sure they are not sedimented in (makes them smaller) with the white paste that can occur from moisture getting into ethanol-laced fuels: it then binds to the brass in the carbs and shrinks the hole sizes. Those holes should be 0.0345" for the larger ones and 0.025" for the smaller ones: with ethanol-laced fuels the larger ones work better at larger size, like 0.0375" to 0.039" instead. You can poke out the white crusty stuff with a stiff wire, don't have to pull the carbs (just the bowls and the emulsifiers). Also check the emulsifier holes on the idle jets to make sure they are clear: if the pilot jets are not Keihin (but Keyster instead) then there will be 3 pair of holes instead of 4 pair. This makes the Keyster idle run richer than it should, so then the air screw needs to turn inward a bit more.
The 750F0/1 cam opens the intake valve at 0 degrees TDC (instead of the +5 degrees of the 550k engines) so the bottom end torque will feel different from the 550 in that it will be more sudden at takeoff. It 'comes on' at about 3000-ish RPM, too, instead of 5500 RPM like in the 550K. This difference is due to the intake tract being much shorter than the 550's version.
