When you worked on the cylinders, did you polish them to a mirror finish? My uncle had a H D dealership, and he used to remind me to make sure that the cylinders (at least on the 2 cycle) bikes had a mirror finish. Greater speed, less heat, I guess.Two-stroke motorcycles are very critical for cylinder to piston clearance. I measured the clearance during a rebore operation by inserting the piston in the cylinder with a long feeler gauge at 90 degrees to the piston pin. Then I'd use a spring scale to measure how much force it took to withdraw the feeler gauge. I handled the piston and cylinder using gloves and/or shop towels to minimize heat transfer.