Hope somebody can help me here. I have a 2006 YZ450 and I was going riding this morning and needed to change my oil. I started it up to get the oil warmed up, it started on the second kick, sounded normal, and when I shut it off with the kill switch, it made a noise, and backfired once. I thought it didn't sound good, so when I went to restart it, it was extremely hard to kick over. I figured it must be out of time, so I tore it down, and sure enough, the exhaust valve was off one or two teeth. I retimed it, put it back together and it fired right up and sounds great. The tensioner is working fine, and the chain looks good, as well as the cams. Anyone have any ideas?