My son bought a 2003 KTM 50 and seemed to run fine. After about 15 minutes it would get hot and loose power. We have replaced the clutch, clutch hub, had the top end checked, checked the woodford keys on both the clutch side and egintion side, flushed the coolant and put in yellow engine ice, put the carb back to stock settings and then adjusted it from there to try to help it as it wouldn't idle at all at stock settings, the idle screw has to be completely screwed in to idle. After 10 minutes it starts running bad and after 15 minutes it's boiling over.
I could sell it fine I think cause it will run fine for 15 minutes but that's wrong and a guy now has all my sons money and my son has had a bike that doesn't run right now for a couple months. I am about the part it out but thought I would see if anyone has any other ideas to try.