My HT engine blew its piston pin needle bearing, and one of the needles managed to get in between the piston and cylinder. The engine still started and ran, but power was way down. I had a spare piston and cylinder, and before installing it, I gave the cylinder a nice hone and put it all together. At first, it started easy, just like the old one, a couple feet down the driveway and off it went. As the the cylinder, rings and piston broke in and mated to one another, compression went up and starting got harder and harder, more resistance when dropping the clutch to start. Now I have to pedal like crazy and get up plenty of speed or else the rear tire will lock up and skid due to the compression resistance. I actually preferred it when the engine had low compression and I could start it within a few feet,with hardly any speed, now it takes high speed and slamming my butt down onto the seat when I drop the clutch to make sure I have good traction on the rear wheel in order to start.