[BigLew]

I had a similiar pfoblem with an I/O years ago. It would idle fine and then either shut down or refuse to accelerate like it should. It kept getting worse as the days went by. Finally talked to a mechanic and he said to check the float chambers of the carb for water. Sure enough. There was enough water in the chambers to preclude anything more than a trickle of fuel across the water's surface and into the engine. I suspected that when it shut down it actually sucked enough waster to simply kill any combustion.

Good luck.