1981 cb750k idle surges when I pull in clutch

[Unclegibbons]

Hey all!
Been tinkering around with this cb project and got it running pretty good. Carbs cleaned, new boots for air box and cylinder side, and it idles pretty smooth when it’s cold, but when I’m out riding it around and say a stop light is coming up and I pull the clutch in the idle seems to soar to 4k or so. If I down shift slowly as I’m approaching a stop and do some engine braking it’ll come to a smoother idle at a stop. This surge happens in neutral and when I pull the clutch. Sometimes it’ll hang at that high rpm and sometimes it’ll gradually go down to a more reasonable idle speed. I don’t have any vacuum leaks and the bike runs great when it’s driving. All through the gears the power is smooth and there’s no real rough spots. Scratching my head a little over this problem. Any ideas?

 

[canorthup]

Hey all!
Been tinkering around with this cb project and got it running pretty good. Carbs cleaned, new boots for air box and cylinder side, and it idles pretty smooth when it’s cold, but when I’m out riding it around and say a stop light is coming up and I pull the clutch in the idle seems to soar to 4k or so. If I down shift slowly as I’m approaching a stop and do some engine braking it’ll come to a smoother idle at a stop. This surge happens in neutral and when I pull the clutch. Sometimes it’ll hang at that high rpm and sometimes it’ll gradually go down to a more reasonable idle speed. I don’t have any vacuum leaks and the bike runs great when it’s driving. All through the gears the power is smooth and there’s no real rough spots. Scratching my head a little over this problem. Any ideas?

I have the exact same issue let me know if you find anything. I close to just buying another set of carbs

 

[L4J]

This is a newer bike to me with with a similar issue. I noticed that that there's no play in the clutch lever so so I'll be be adjusting that. I'mThinking that it's at least part of of the problem. If that doesn't fix it, I'll be looking looking at throttle cable where where it connects to the carbs.

 

[92ujm]

I know you cleaned the carbs I was having the same problem it would idle from 2500 to 3500 nothing seemed to work I checked for air leaks vacuum leaks tried adjusting pilot needles. Nothing so I pulled out the carbs and cleaned it out as I was reinstalling it I moved the vacuum line from carb 2 to the petckock and the hose was broken towards the bottom couldn’t see it from top or make any changes to engine when spraying. Runs perfectly now don’t know if it was carbs or hose but worth checking.

 

[Mwood1129]

Hey all!
Been tinkering around with this cb project and got it running pretty good. Carbs cleaned, new boots for air box and cylinder side, and it idles pretty smooth when it’s cold, but when I’m out riding it around and say a stop light is coming up and I pull the clutch in the idle seems to soar to 4k or so. If I down shift slowly as I’m approaching a stop and do some engine braking it’ll come to a smoother idle at a stop. This surge happens in neutral and when I pull the clutch. Sometimes it’ll hang at that high rpm and sometimes it’ll gradually go down to a more reasonable idle speed. I don’t have any vacuum leaks and the bike runs great when it’s driving. All through the gears the power is smooth and there’s no real rough spots. Scratching my head a little over this problem. Any ideas?

Have you checked the cables ? The clutch cable isn’t interfering with throttle cables ??
Just a thought