Carter thermoquad?

the idle speed adjusting screw is missing in the later carbs. Maybe if you're really handy, you can drill and tap that part of the casting, which has been left unmachined. I've never done it, but it looks doable. IIRC, the vacuum advance port is on the right (passenger) side. If you turn the carb over you will see the venturi end of the port, at edge of throttle blade (primaries closed).
I agree with previous poster, a few pictures would be helpful.