The engine idles nicely until it heats up to the point that the fan starts, once that happens I have to adjust the idle speed up to 2k rpm or it would stall and the meter falls to 1k rpm around every 2 seconds as if it missed a few firings. Otherwise it does not lose power noticeably when hot. Carbs are balanced, it's an engine with around 70 000 km and has been like this ever since I had it (around 10000km). Is this normal with this milage or is there something I can do about it?

Possibly valve clearences?
Have you checked them lately?

Have to double check that with the mechanic, I told them to but they probably thought "what for" and just skipped it. I'm also suspecting blowby because of oil in the airbox and it's eating around a liter of oil in high speed operation per 1000km. I did that thing when you keep it 5000rpm for 15 seconds or so and the rev it up suddenly and there is black smoke not white/greyish. Compression is uniform around 10 kg/cm2.

WHy is it sittingon idle when actually is that hot? I'd turn the bugger off!!

I get the feeling an HRC air try might help and shield the carbs from the high heat if you are in high ambient..

Valve clearances..lol - Any mechanic that said "Why?" needs to go and sell ice cream...

HRC air tray yes or I could make something out of insulator sheets, the ones used to insulate the fairing.
He didn't say that it's not needed I just suspect because of the valve covers looked undisturbed after the initial service.