It'll stick out pretty far into the carb throat. When you tighten the main jet emulsion tube, it'll bottom out that part.
Closing the choke and the engine revving up is a vacuum leak. It has the air through the leak and when you choke it, more fuel is introduced. Need to take the intake off, check both ends and the carb flange for flatness with a straight edge, then replace the two O-rings. This is a very common problem. The carb flange ears tend to bend in over time, but a few licks with a file will have it sitting flush with the intake again.
The story of three wheels and a man...