05 grizzly660 problems?

[zr600]

My 660 griz won't start it just backfires through the exhaust and the carb, last time i used it a couple weeks ago it started just fine, what would cause this it has spark, and the motor just got a complete rebuild from the bottom up. What causes a backfire?

 

[rocketron]

Sounds like a timing issue. Did you replace the timing chain during rebuild? The Grizzly's that i've rebuilt the timing chain was pretty much wore out in all of them.