When I first bought it it ran fine. Then I was riding at someones house for a couple hours, it started backfiring. It would stop running and it got really hard to start even when it was a little warm, and this problem kept getting worse. Now it is almost impossible to start and back fires a lot and when it's running, it will cough, stall and even stop running when coasting and it is warm. I cleaned the carburetor, has a slightly used plug and replaced the main jet and it still won't run right. I think it's the spark coil or magneto coil. Any suggestions that you think will be nice. Thanks.
I also think that the timing may be off too.