No idle change with air screw adjustment

It is my understanding that there were at least 3 versions of the vm29s offered. the A2, A7 and A12. There should be an ID stamped on the flange either below the choke lever, or on the other side of the carbs something like the following
29
A2 - this second line could be any of the other types noted above

IIRC the throttle valves have a larger cutaway on the A12 than the other 2 do. The A2 has a smaller pilot jet (17.5) than the others and a smaller needle jet than the others.