It is the round type. I do not think it is a clogged line due to the fact that after the pump cools down it runs fine for 5 or 6 minutes before it quits. Then the
pump does not run when S1 is in the run/prime position until after I wait for about 15 minutes. If the fuel line was clogged wouldn't the pump still run?
Have you felt the pump? Was it HOT? Or just warm? If you haven't felt it, you don't know its overheated.
In post 63, LITD is right. It often happens, that some sort of trash plugs up the pickup tube. The set runs out of fuel. Then the trash slowly drifts back to the bottom of the tank. And that take a bit. 5 min would be about right. Then the whole cycle starts again.
Now my question to you is this. When the set stops, is it the typical running out of fuel type of stopping? Engine speed dies off, it may sputter a bit. Or does it just stop. Like being turned off? Because if it just stops, like being turned off, then its not a fuel blockage. Do you get and idiot lights?
If you really think its the pump, remove the in put and out put lines. Install two temporary lines. Stick the input line into a jar of fuel. Stick the out put line into the jar. Turn the S1 on to prime, and drink a beer or two. Give it a long run. This is almost the same as LITD's method in post #64, but this way you don't have to worry about emptying a container. You don't even have to stay there. Just keep an ear out for it.
Also, the filter on the electric pump. Have you changed it? It also might be plugged up.
Your one hour test run is not much of a test. If it is a trash problem in the fuel tank, it may, or may not, happen always at he same time frame. Have you inspected the fuel tank?