timing issue i think

[RingoYFZ450]

I need your help. I did the cam mod a week or two ago and everything was running great. When doing the cam mod I checked my valve clearance and noticed they were too tight. I bought new shims and now the clearance is back within spec. However after putting her back together it wont start and backfired really loud like a f#$%ng shotgun. How do I make sure my timing is right?

[YFZer]

Sounds like you went back more than one tooth on the exhaust cam, its very easy to do on the dual cam setup. Recheck the timing marks and the exhaust cam should be rotated clockwise one tooth for cam mod I think.