Idle problems when hot

Hi all. I recently got a 1977 KZ650 B1. All stock. It's having trouble idling when it gets hot. It runs great and normal until I've been riding it for a while. It seems to happen faster when it's warmer out and the problem takes longer to set in when it's cooler out. The symptoms are similar to when it's not warmed up and I have to feather the throttle to keep the idle at a healthy RPM (~900-1,100?)

My guesses are wrong spark plug heat range (Currently has NGK B7ES) or bad valve clearance? I was hoping someone had something easy to check before I check the valves. It runs great, starts easily, but once it reaches a certain temperature then it seeems to have trouble idling but I can ride it without noticing, just when I stop and wait that I notice the RPMs starting to drop.

Any ideas or things I should try out?

Thanks!

Check the valve shim clearances, metal expands when hot, making your engine act this way.

Valve adjust can also drastically affect cranking compression .
in thousandths of an inch anything less than .005" put the next thinner shim in .
.008" is about the max clearance . .006" if you like to check often . Any less and you risk closing up a valve through inattention and covering up a marginal valve clearance with carb sync , ignition advance and idle adjustment until you actually hold a valve open . Translation ? neglect your valve adjust = $$$ .

These links are to some excellent advice from RonKZ650 as to dealing with changing shims on a KZ650.

www.kzrider.com/forum/2-engine/504154-re...-measurement-#504154

www.kzrider.com/forum/2-engine/305725-re...-advice-neede#305725

www.kzrider.com/forum/2-engine/221680-revalve-clearance#221680

www.kzrider.com/forum/2-engine/146192-revalve-shims#146192

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If not already done, should also study relevant sections in the official Kawasaki Service Manual with regard to camshaft timing, shim replacement, etc.

Let us know if needing a free manual download.

Good Fortune!

I would lean the pilot system just a bit. Turn your air screws out a good half turn moor and see if it makes a difference. That costs nothing and you can screw them back in if it does not help. That is just one option to try. Are you runing a 20w50 oil in your bike? (Mike)

Thanks for the replies.

I'm gonna check my valve clearances, attempting to save 20 hours by using the method outlined by RonKZ650 in those links Patton posted. I have a factory service manual and was a little intimidated by the camshaft removal and installation since I've never done it before.

I need to buy an inch pound torque wrench for the camshaft caps, I have some feeler gauges. Any other special tools I need? How do I get the valve lifter off? The book just says use a "suitable tool" and shows what looks like a suction cup?

Thanks!

It sounds like all the other kz650s that are stock or close to it.
They came lean ,,, VERY LEAN.

Plus the gas they sell us now a days is only 90% gas in NY.
(Going to 85% here soon)

I have seen a guy named WiredGeorge answer a few folks carb questions .
Seems like a nice guy and knows carbs inside out.

If you find him , ask nicely.

To lift your lifters out (if you have to) use a magnet.
Thats what they made old speakers for.

Check carb holders for leaks. They may start leaking when they get hot. Ed