Motorcycle Repair: Curious Idle, vacuum ports, vacuum tube

Question
Hi. I have a 81 cb750, which I know is a model you don't cover, but I'm hoping that my question is general enough for it not to matter.

The bike will start mostly fine, usually a little reluctant at first (my choke cable is stuck, so I have to run it a bit rich). Once it starts, it will idle fine, right about 1k, but over two or three minutes it will slowly climb to 3k. There is a spot for a vacuum tube near the mouth of the number two carb, which has to be plugged for the bike to idle. Does this have to be connected for the bike to idle correctly, or is it something else? Thanks.

Answer
Yes the vacuum ports should have a screw in them, they are only used for synchronizing the carbs, unless one has a connection to a vacuum shut-off on the fuel system.  A choke cable is about $10, I'd fix that too and have the engine run properly.

Good luck,  Jan