just got my 07 back together after replacing a few gears in the bottom end. go to start it, and it backfires really hard and blows the tb boot off the head. it seems like it cranks over easy until it gets to the compression stroke and then struggles and stops the starter. i can get it to run well if i catch it right and it runs ok, so i'm thinking its not timing. the backfire though, makes me think timing, so im not sure. i didn't take the cam out of the head when it was apart, so that should be the same. the only thing i took off was the cam gear. is there something i could have messed up in the decompression mechanism when i reinstalled the cam gear?