I'm sure Jim's right about the throttle shafts. If you had a bad enough vacuum leak on the intake you'd probably have really high idle. To check you could just cap the carb's vacuum hook-up, the vac advance shouldn't kick in under 1500rpms anyway. But if it's the shaft that loose, you can't meter the air that's goining in.

Also don't discount checking for mechanical hangup: number one the throttle butterfly, make sure they both open the same amount with the throttle input, engine off.

Check damper fluid's quantity and appropriateness. Whatever you've got in there make sure it's the same for both carbs. Unless you're confident in your trickery. Make sure the piston ass'y is clean, and coat the shaft with some light oil.

Check that the needle isn't abraiding the jet sleeve on the way up, and that the jet is centered in it's bearing and not protruding into the throat.

Or just give the throttle shaft a tug and if it wiggles you'll know the score.

Good luck,
-Sean
--
1966 122s; 1970 142s