Hey, my bike (2009 250SX but that doesnt matter) siezed this morning- the second ride since I rebuilt it. I was pinning it in 5th gear (high revs) for about 30sec when it lost power for half a second and the back wheel locked up . The bike had been broken in fully, and today it had been warmed up and ridden for about half an hour before it happened (so it wasnt a cold seizure). The stock main jet was a 158 and with the jd kit its now 165. The plug had a nice tan / light chocolate colour after seizing, so I'm pretty sure it wasnt lean on the main jet. we took it apart and the ring gap is 0.16" / 0.4mm for both rings after seizing. This is on the large side, so its not that. the cylinder is scored deeply and the brand new OEM piston is scored on both sides. The scores are in the same place as the first piston the bike had as you can see in these pictures, the old piston is on the left and the new piston is on the right: http://i942.photobucket.com/albums/ad268/mikekx/IMG_7398.jpg http://i942.photobucket.com/albums/ad268/mikekx/IMG_7401.jpg http://i942.photobucket.com/albums/ad268/mikekx/IMG_7394.jpg http://i942.photobucket.com/albums/ad268/mikekx/IMG_7397.jpg and this is the main score on the new piston: http://i942.photobucket.com/albums/ad268/mikekx/IMG_7408.jpg What could have caused this? running a ratio of 50:1? I read this really good article on the ratio and it said that you shouldn't just run what the manual says, but what you should run depends on how you ride. I ride trails and just mess around, but because of the way I ride its more like desert racing with a little bit of just cruising. should I run 25:1 and re-jet? Whats the issue here? Mike.