XP backfireing

[ChrisM8]

Friends 800 XP started back-fireing @7500rpm and then will only rev to 8000rpm or so, then its like its missfireing or hitting a rev limiter or something?? Changed the plugs on the trail, light tan on both, and it seemed to get rid of the back-fireing, but still only revs to 8 grand then hits that limiter, and coughs and sputters. Is there a limiter on the sled?? The kill switch also stopped working while we were riding, not sure if that is part of the same problem? any ideas were to start looking?

Cheers
ChrisM8

 

[SilverGriz]

The sweet spot on the RPM's is 8200. I think the rev limiter is like 8500.