With the electric fuel pump there has to be a return line, they develop a lot more pressure than mechanical engine mounted pump. There is a bypass valve before the carb. The constant fuel circulation prevents vapor locks. On the inside of the drivers side frame rail there should be 2 lines, on my 86 the fuel pump is there just rear of the front wheel in front of the transfer valve.
Carb fuel supply is usually less than 20 pounds, electric pumps put out close to 60, perhaps pressure relief/bypass valve has a problem or could your return line have gotten damaged, easy to check.
My understanding is electric pumps put on motorhomes because gas tank further back, also assuming your motor firing on all cylinders, spark plugs extremely difficult to change.
I had similar thing happen with carbereted motor, would not start, cranked for a long time, finally fired and exhausted vapor exploded splitting muffler.
