First, I would like to thank you guys that have contributed to this forum. I recently did the BK/GB Mod by following the instructions. Worked great! Next, I decided to try the 450 cam in my 2001 yz426. I put in the 450 cam, installed the proper shims, checked clearances and put it back together. The bike fired for a couple seconds, then died. Now it just backfires when trying to start and does not run. I thought the timing must be off, so I checked the timing marks and cam positions (lined up with the "I" not "H"). Timing is correct and cams look like those in the picture for the mod. My cams have 14 pins between marks, but I noticed one guy said that he only had 13. So, I turned the exhaust cam so that 13 pins were showing, but that looked way off from the right side of the bike. Moved back to 14 pins and cam positions. The cams look right (I even rechecked clearances and cam positions after installing the cam chain tensioner). One shim was really tight. Could that cause a valve to stick open? Any ideas???