Try running a new piece of fuel line directly from the engine to your gallon of fuel. If the problem doesn't surface, the problem is your tank. Take the tank out, run the engine again - this time with the tank outside the plane. If it happens again, you can rule out fuel foaming, so do like rreiss said, recheck all of the tank lines for pinholes.

If it IS fuel foaming, reinsert the tank making sure the NO part of the tank is touching anything but padding. If it still foams, try adding one short squirt of WD-40 to your jug of fuel.