Just a guess that your gas cap may not be venting air into the tank as fuel is drawn out.
When it starts to stall try loosening the fuel capdoes it recover? OR after it quits do you hear a small rush of air into the tank from around the cap?
I have sean the cap vent hole crust up with dirt or sometimes the vent spalsh guard/ foam in the cap is missing and someone puts a peice of rubber or some gasket material in the cap that covers the vent hole.
Just a place to start, what engine does it have?
Good Luck,
Friiy
