Had a similar thing happen on one of the 5 ports I owned. Just shaved a few thou of each pinch bolt end as MM suggested and it worked sweet as. Check the bottom carb "O" ring (the brown one in the crankcase body) before you reassemble, as the movement you have been experiancing in the carb can sometimes chew this "O" ring up a bit. Now you have a better fit with the pinch bolts just remember not to do them up too tight, or you can damage the carb throat.