Thanks Al. I do have it installed correctly. This pump has a pressure sensor on the output side so it shuts down when it reaches about 2 psi, so it's not an overheating problem. Even when I have the output hose disconnected, it shuts down before it pumps any fuel, as if the output side had developed 2psi--even when the pump and input line are full of fuel. It will pump fuel when the input and output are at the same level.
I have been discussing it with Walbro. The first response was that it should work. He is going to talk to the engineers about it and get back to me.