KZ200, no idle warm, hard to start warm.

LasseT wrote:

I did a new test.
Cold engine, open throttle 10bar
Warm engine, open throttle 10,5bar

That equates to 140psi so you can cross low compression off your list of possible causes 

Check for overly rich. Is choke plate fully open? Mixiure screw adjustment? Carb bowl fuel level? Correct size pilot jet? 

LasseT wrote:

@ Scirocco
ok, I'll check the valve clearence, but wouldn't you here if the clearence is to small (valves not closing) when you pull of the gas handle?
I guess it could also be piston rings, but it doesn't smoke black.
 

If you had bad piston rings, it would be burning oil and the smoke would be light blue. Black smoke would indicate a very rich fuel mixture and/or a weak spark, leading to incomplete burning of fuel (which would look like a rich mixture).

Ok,
now I have changed spark plug to NGK B7ES with no improvment.
I've added a sound file.
 

I've got no reply on the sound file.
I've tested the carburettor and manifolds for leaks (start gas), but no signs of leaks.
Is it worth looking for another carburettor?

The video file will not play for me. I would not replace that carburetor until you are sure it is the problem and it is not fixable.

It could be as simple as a jet came loose and fell into the bowl. Perhaps the float has a small leak and it allowing the fuel level to get too high. As mentioned earlier, perhaps the choke plate has come loose.

I know you said the valve lash and ignition timing were checked before, but I think it would be worth the time and trouble to recheck them , since this is a new problem. If they prove to be within the specified range, then I suppose a thorough look at the carburetor is in order.

Perhaps the ignition coil is going bad, and as it gets hot is unable to provide sufficient spark. I would probably put this last on my list of suspects.