Extremely high idle.

1980 650. Just recently replaced the manifold boots because the originals were cracked and leaking air. Also took the carbs off and replaced the original idle circuit screws with new ones, they have the same size hole. Pulled the tops off to inspect the diaphragms on the plunger, they don't have holes in them. None of the cables are getting stuck. Everything snaps back to where it's supposed to without a hitch. The idle set screw in the middle doesn't change anything when it's running. I didn't mess with any form of mixture tuning. Bike starts up just fine but then immediately climbs to 7k rpm, and sits there. Killing it causes a backfire. Anyone got advice?

 

Do you mean when you turn the idle set screw when the engine is running it has no effect? Sounds like it's running weak.

 

https://www.xjbikes.com/forums/thre...of-a-82-xj550-maxim.129717/page-5#post-691153

 

Make sure that the throttle cable is set down inside the holder on the cab side. Sometimes it gets hunt up on the top edge of the holder and that will cause a high rpm on start. Did you do a bench synch of the carbs? At the butter flies almost closed with just half or one of the small holes on the bottom of the inlet to the carbs showing? As @Franz mentioned, change the idle screw to the left or anti-clockwise and see if that has any affect.