Hi,

Is this engine a rear carb version of the 3w-75? If so, was it spitting any excess fuel out the carb? The symptoms and age of the engine (runtime) would suggest a failure of the reed valve. The rear carb version has a reed valve. I believe that the side carb is also reed valve rather than piston induction, but I don't know for sure since I have never had one apart.

Hope this helps

Elson