I have an 89 250 Moto 4.I went to take it for a run this morning and it won't start.It turns over 2/3 times,then a pop out the exhaust.It keeps doing that.I took the tank off and drained it because it hasen't been used since last fall.I also took the carb off,took it all apart,and blew it all out.Put it back together,added fresh gas...same result.The air breather had gas in the bottom of it too.

Any ideas?

 

sounds to me like timing..

 

How do I check?