I know its not a dirt bike, but I assumed you have experience with 2 cycle engines. Recently, it started sputtering and making noises when riding past ~15 mph(about 1/2 top speed) the problem got worse until about 5 mph it would back fire and completley loose power but it would never die. I opend up the carbeurator and cleaned it(lots of black stuff in the bottom) I put it back together and now it dosent wanna start, im gonna replace the gas and see if thats the problem but not shure.. a friend, whos mechanically inclined said it was lean from riding it but i really am at a loss here, any help will be greatly apreciated!