I think Pops has a very good point. It sounds to me like the float in your carb is letting in too much gas. I'd inspect and/or replace it, (along with the inlet needle valve, seat, etc. if these apply here) then make sure it's adjusted properly so the bowl doesn't overfill.
Something tells me this is not a serious mechanical problem ... just one of those little "forehead slappers" that drives you bonkers for awhile.
I once had a snowmobile motor that defied any and all attempts to make it run for more than a mile or two. After I sold it (too cheap) I found out that that particular model came from the factory with the "in" and "out" gas lines reversed.
Hope you get to the solution soon ...