1998 TRX 450 ES Foreman backfires on quick slow down from high speed and while down shifting on a down hill climb.

I also noiticed on my air filter change an odor of gasoline.

Any help or reccomendations would be great.

 

Check for leaks in your exhaust and exhaust gaskets, do you have stock jets in it?

 

Might be time for a good carb cleaning, backfire on decel is usually a lean idle mixture, when the throttle is closed, it gets most of its fuel from the idle circuit, if that is set too lean, or is dirty and restricted, you will get the "pops" from the motor while it slows down. You can try opening up the idle mix screw a quarter turn at a time to see if that helps, but I would also follow Pinkfloyds advice and check for an exhaust or intake leak, that would also lean it out and cause the backfire you are hearing. spray carb or brake cleaner around the carb and intake boot while idling, if it changes idle speed, you are pulling air in from that spot. But a good carb cleaning and checking the settings is always a good idea once in a while, if you havent had the carb apart since 98, may be time.

 

Dirty carb... Clean clean clean