KZ250A missfires on high revs then dies when hot??

Hi! Im a new member on here, and this is my first post and question.

I just baught a old 1981 KZ250A (twin), and i hav the problem thatI cant get it to run clean on higher revs,
and as soon it gets a bit warm it looses power more and more, finnaly I have to give it full throttle just to keep it alive and get only low rpm untill it dies completly. If I let it cool down, it fires up just fine again, but still vit the high rev issue.

Anyone have any ideas?

I baught anothe 1979 KZ250A for parts, and I changed the whole engine, exept ignition coils, carb and stator. It has to be in one of them i guss?

I aprechiate all help i can get!

Greatings from Sweden!

It could be the battery or the ignition coils. The bike needs a good fully charged battery to run right.
high beam load test: engine off, high beam on, battery charged --- a good battery will drop from 12.6+ to about 12.2 VDC.
A simple check for the coils is to ride the bike at high speed, then stop & feel them, press hard with your fingers --- they should be warm, not hot. Or do the ignition coil tests outlined in the manual --- check them cold & hot.

Have you checked valve lash? If they have not been checked and adjusted in many miles, there may be little or no lash, which can cause the symptoms you describe.

Might also be a kinked fuel line or a clogged or improper fuel filter.