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Discussion Starter · #1 ·
Hi guys,

A couple of months ago i upgraded from an 08 wr250x to an 06 crf450r with an athena big bore kit. i just spent this weekend doing the clearances which were a little tight but are now within spec. While in the motor i noticed cam timing advanced by 1 tooth on the cam gear. Now ive done some google and forum searching and i couldnt find anything on this. Cam timing is now stock and clearances are within spec but the bike is now backfiring when kicking, once started it seems ok. It never used to backfire before i changed the timing back to stock. I had the bike on a dyno before i changed the timing and clearances and it got 42 hp, nice curve with no flat spots (according to the guy who dyno'ed it). Spark plug is good and ill do a compression test this week as well as another dyno run.

Is it normal to have the cam advanced?
Is it to do with the big bore kit?
Any ideas on whats causing the backfiring?

Thanks,
Mark
 
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