Idle varies a lot between cold and hot 1978 KZ1000

The idle level changes drastically on my KZ from when its started cold to when it heats up.

When its hot I have to spin up the idle dial so that the bike doesn't stall when I let off the throttle.

When its cold, still having the idle level set from when the bike was hot, I have to spin that idle dial quite a bit to get it from around 5000RPM to around 2000RPM.

If I set the idle to anything lower than about 2000RPM (whether hot or cold) the bike tends to stall unless I hit the throttle when the clutch is out.

Possibly the advancer is sticking. Using a strobe-type timing light, should be able to watch it move back and forth as rpm are varied.

Good Luck!

Just a thought here... are your rubber carb holders, between the carbs and the block, leaking?

Best of success.

bill_wilcox100 wrote:

... are your rubber carb holders, between the carbs and the block, leaking?....

If needed, new carb holders are listed at Z1E
carb holders

And another possible source of air leak
vacuum caps

Good Luck!

If not already done, would check valve clearances and assure being set to factory specs.

Might be too tight, so as to be sealing when cool, but begin leaking at normal operating temp.

Just thoughts.

sounds like a bad air leak spray some carb or brake cleaner around the intake manifolds, if the engine chages in r.p.m you have just found your leak

you have described the exact opposite of normal.

after any carburetor/airbox modification from totally stock a motorcycle will usually need the rider to turn the idle UP when it is cold to keep it running smooth and as it heats up the idle needs to be turned back DOWN to a lower idle speed.

as the engine builds heat the efficiency level goes up and therefore needing LESS gas/air mixture to run when at full operating temperature.

so your description leaves many unanswered questions because it does not add up.

start at the beginning
leak down test.
compression test
new spark plugs
reset the points
reset timing
lube the advancer
re set float heights
synchronize carbs at idle AND 2000 R.P.M.
lean idle drop all 4 carbs

check for loose bolts and tight spots on the carb bank dealing with the throttle cable, slide lift pivot, assure all slides fully seat when closed.

and by the way- fire the mechanic that got you to this point.

timebomb33 wrote:

sounds like a bad air leak spray some carb or brake cleaner around the intake manifolds, if the engine chages in r.p.m you have just found your leak

not even a close guess with this description he has given