Topic: Engine Idle High...

[TPS]

I have a 1977 CB750K and I finished rebuilding the motor and have assembled everything to spec... the problem I am having is the bike idles too high.  After idling for about (2 - 3 minutes) the bike just jumps up between 4k - 5k RPM.  I have checked the timing, points, coil pack, valve clearance and I checked for vacuum leaks.  I couldn't find anything.  It starts up beautifully but once it gets warm, it idles high.  I have backed off the idle adjuster screw knowing that it would choke the bike and it maybe drops 200 RPM.

I'm at a point where I'm stuck.

Any suggestions would help!

Thanks,

TPS

[HavocTurbo]

Did you check your throttle cables?

Just a thought.

[DammitDan]

Did you bench sync the carbs when you reassembled them?

It really does sound like a vacuum leak...  How did you go about checking for a vacuum leak previously?

[TPS]

I did check the cables and they don't seem to be sticking or causing it.

I used an old school method of checking for a vacuum leak.  Well a couple of things...  First I was told to plug the intakes and if the engine dies immediatelty, the it wouldn't be a leak or the engine would run for a bit more.  I took a propane torch (small blow torch) and followed around every gasket.

I found tiny traces of air bubbles on the lower block gasket on the outside near cyl. 1.  But not for seem reason those bubbles are gone and there is no leak or at least I can't see one.  Do you have any good suggestions on how to check for vacuum leak aside from those 2 methods?

Thanks...

[BobbyR]

I have a 78 so we have the same carbs. There is a high idle cam that pushes gainst the idle adjustment screw when you pull out the choke. If that were out of position it may cause what you are talking about. It is a long shot, but you seem to have done everything by the book so far. Look for something that may be bent.