I have a 98' foreman 450 and it has a major back firing problem. very randomaly it back fires. Its super loud, like a gun.. and If i am giving it gas in 2nd 3rd, or 4th let off and give it gas again it will hiss for a minute until i let off the gasl. It sounds like the hiss is coming from the rear end or maybe the exhaust. somewhere in the back of the bike.. PLEASE HELP...

 

pimpin 300ex you have a head pipe that is crack and sucking in air that why it back fires. It will suspersed to a new one like off of a 2000, you will also need the clamp that goes around there, you'll know when you look at the parts. Don't for get to get a new exhaust gasket.