I've got a 660 with a high compression piston and full pro circuit exhaust. the last two times i've ridden it the exhaust was popping (don't know the official word) like crazy. When ideling it's fine, or when accelerating it's fine also, it only pops when I let off the throttle. Any ideas as to what this might be? It's super loud, sounds like a gun and it's maybe two or three really loud pops each time I let off the gas.

 

may be a leak in the exhaust letting air in

 

What size pilot jet are you running,,,and how many turns on the screw

also, be sure the exhaust isnt leaking where it mounts the the engine,,,like squeege said

 

Yeah my Raptor was poping when i let of the gas. Its most likly the mixture. Try putting the choke on a little and if it goes away then its your mixture. well im sure you know that the choke will decrease how much air gets in so its the same as making it richer. But don't ride like that make sure you change your jets of mixture screw

 

Thanks for all your help. I'll let you know what I find out.