could be...
My son's KX125 ran great when its compression was around 125-130...
then it really started loosing power when the compression was around 115 and wouldnt run when the compression dropped to 100-110.
Upon tear down we found the ring was really worn and the ring gap had 'grown' to about 1/8 of an inch allowing a lot of blow by. Also, with the ring that worn, there was little ring tension left. But the Cyl and Piston still looked great and were within spec. He has an unreal number of hours on it, I wouldn't even guess how many.