1981 KZ650 Misfire at high rpm

Greetings from Germany!
I do have a problem with my 1981 KZ650...
But from the beginning:
It is a 1981 model with the engine of a 1979 model, i don't know why the enginge got switched, but the former owner also switched the ignition, because there is fitted an electrical ignition which was not available at the 1979 models i guess? The ignition timing adjustment is mechanical, should it be that way?
Now to the main problem. The engine idles fine so far apart from that when i release the throttle the engine needs a few moments to get to 1500rpm. The engine speed stays a 2500-3000rpm at that point before it normalizes.
When i drive i have the problem that it starts to misfire at higher rpms .Thus i am not able to go faster than 90kph (55mph). The stange thing is that i can rev it up to the red line in the first and second gear without any issues, so the problem with the misfires only appears at the 3, 4 and 5th gear.
I already cleaned the carbs and checked for the right size of the jets -> Everything is fine here!
Regardless of how i adjust the carbs, lean or rich, the problem stays.
I really don't know what to do now. Does anybody had simmilar problems yet?

Thanks a lot and excuse my english, i am not speaking english a lot.

Grtts
Ferdinand
 

Welcome to the forum nandolino. Your engine could have multiple problems like:

Wrong ignition timing, like breaker points gap and/or an stuck ingnition advancer.
The carb boots are cracked and leaking, so your engine is running on a lean air/fuel ratio.
Your valve clearence is near zero, so some valves could stay open = less compression.
and get the service manual. 

kzrider.com/modules/ServiceManuals/Kawas...Service%20Manual.pdf

 

When reading your post I immediately thought air leak/cracked carb to head boots.
Classic symptom of this is the throttles response when closing is slow to back down in revs. This is commonly called hanging throttle.  You can easily check this by spraying carb cleaner around the boots when the engine is running. Any change either increase or decrease in revs means they have a leak. 
Timing advance for electronic ignition. can be either manual using the stock atu or electrical using a gizmo box or igniter box depending which electronic ignition is fitted. 
If you have stock atu ensure the centrifugal weights have free movement and do not stick. As engine speed increases those weights should open under centrifugal force and close again under spring force as revs drop. 
Those are the two most likely causes and luckily the simplest to check so do those first. 
If they both check out OK you'll have to dig deeper and valves is next suspect. 

Thank you for your reply!
I changed the intake head boots ans also sprays some break cleaner while the engine was running but the revs did not change at all. 
Also i took of the valve cover and had a look at the hydraulic lifters, these were fine to so i don't think i have any issues there. The compression of the engine is fine to, it is about 9,5 bar (137psi) at every cylinder.
The carb boots are fine too, i checked the carbs like 5 times now

I really don't know if the ignition is stock and i don't know how to how to tell them apart but i already changed the pickup coils when they were broken.
I will have a look at the centrifugal weights (which i have so i guess i have the stock ignition?) even though the engine does not misfire an high rpm in the first and second gear...

Thank you so far
Ferdinand

Can you upload some pics of your bike and ignition timing plate. Where are you located in Germany?

Here is a pic of the ignition. Does it help?
i am located in Hamburg, the bike stands near Norderstedt. Also that’s why I can’t get to it every day.

If the ignition coils are original to the motorcycle, they may need replacing. Ride the motorcycle to highway speeds then stop & feel the coils. press hard w your fingers >> should be warm; not hot. don't get burned by the valve cover. My 81 650-CSR was running poorly at high speeds: the coils were very hot to the touch, so I installed the green Dyna 3.0 ohm coils. But you can install the grey Dyna 2.2 ohm.

Timing advancer. as normal maintenance >> clean, lubricate & check the timing advancer. Separate the rotor from the body & be sure to fill the groove w grease.  I think I used high temp wheel bearing grease the last time. or maybe brake caliper grease.  Reassemble & check the action of the advancer: turn the rotor then release >> it should snap back to the static position. An FSM pdf is readily available.

Hydraulic lifters?

Is the airbox installed and fully sealed?  What's the condition of the air filter?  And what about the plugs?  Do you have a healthy spark on each cylinder?  After a cold start does each cylinder warm similarly?  Spraying water on the header pipes during start, or touching lightly right after a start, will show if you have any cylinders that are not firing.  

Hey guys,

i am at vacation atm, will work on the bike after that. 
I already replaced the plugs, every cylinder gets evenly warm. The problem only occurs at high rpm. The air filter is new too, the condition of the airbox is fine too.

Greets from Greece