I would think that it could run that long if you weren't real careful to get the vent pipe right up against the top of the tank. Even 1/4 of an inch low would give you some run time with the muffler pressure coming back through the pick up line.

I had to laugh when I read your post because it is almost the exact same way I lost my first plane. I was climbing out on takeoff when the engine quit. Had to make a hard left turn but unfortunately the 100 ft pine tree had other ideas. My plane wasn't damaged too bad....that is until I payed a guy to cut it out of the tree for me. It hit the ground pretty hard once he cut the branch!

Jeff