Noticed the jetjon running a little rough and had a hard time getting any throttle response....hmmmm....Got home and did a compression test, rear cylinder was way low. Pulled the top end off and found a chipped piston. The cylinder walls are still in great shape, one has very slight scoring that I can feel with my fingernail barely and the other is perfect, a good honing should take care of them in preparation for the new pistons. I don't know what caused the rear piston to go, I am running premix gas at 50:1, possibly the carb was lean or fuel pump issue? I am going to rebuild the carbs and do a leak down test once everything is put back together. Any other suggestions to finding the reason of a blown piston? Also the cylinder head has some pitting and damage from the piston would it still be ok to use if cleaned up?