KZ650 will not idle after cylinder head change

Repeating myself again...

A hanging idle is typically from a lean condition, most likely caused by an air leak. Leaking intake boots at the head and/or carb boots to the airbox are often the cause. Spraying junk on the boots in an attempt to find air leaks is an unreliable method.

:S Given the option to vacuum synch my carbs after an insignificant(?) change (one shim up/down .05mm), I'll do it.

If one refuses to take all the steps called for in the manual, then the desired goal will most likely become impossible.

Nessism wrote: Repeating myself again...

A hanging idle is typically from a lean condition, most likely caused by an air leak. Leaking intake boots at the head and/or carb boots to the airbox are often the cause. Spraying junk on the boots in an attempt to find air leaks is an unreliable method.

+1
Especially true if they were not hanging up before and the cables have been eliminated as a cause.

Bench synchronizing will get the carbs close enough to start the engine. If that got them exactly where they needed to be before, you were extraordinarily lucky. Don't count on that happening again. The new head will necessitate small changes that only vacuum synchronizing can provide, but this cannot be done properly until the engine can idle correctly.

Just a point to check, when you put the cables back on, did you make sure the return cable was fully adjusted down with the throttle closed? This can cause revving high when throttle is bliped open, but should settle back down after a while

Tadyccs wrote: I replaced the cylinder head on my 1977 KZ650 because of a small crack in the old head. The bike ran fine just had an annoying oil leak at the crack. I understand these motors very well and have spent considerable time working on these but now I am at a loss. I got the replacement head and replaced the valve seals. Springs, tappets, shims were all good. It has a Dyna electronic ignition. I checked the valve lash and after a couple adjustments it is in tolerance. Put the motor all back together, shot some starting fluid in the carbs and it started. I would have to keep on the throttle to keep it running as it would not idle on its own. I adjusted the throttle screw but all that would do is rev the motor and eventually it would die unless I keep on the throttle. I sprayed carb cleaner on the rubber carb holders but the RPMs did not change-no air leak?
I retimed the cams again this morning but have the same issue. When I do get it to sort of idle at 1500-2000rpms and rev the throttle the RPMs race way up 4000RPMs. I have to back the throttle screw way down to lower the RPMs.

What is puzzling is that it did not do this with the old head so I believe it is not the carburators. Most posts on this idle issue say, clean the carbs, make sure the cams are properly timed, check for air leaks, sync the carbs. As I said this was not an issue when the old head was on it so carburator problems , I believe, are not it.

Any ideas?

I didn't read any other replies so if this was mentioned already.... Check your valve lash.