Guys installed electric fuel pumps to try to eliminate the issue of hard starts (because they don't know how to start it) after the truck has sit for a few days when the carburetor float bowl empties.
With an electric fuel pump, when you turn the ignition key, the pump starts pumping immediately and will fill the float bowl before trying to start the engine. That way, the engine will start right off without having to crank the engine over a few times before trying to start it.
The drawback to electric fuel pumps when used with a carburetor is that they could over pressurize the supply to the needle valve in the carb, causing too much fuel to enter the float bowl, which ends up getting sucked into the engine & diluting the oil. Aftermarket bolt on electric pumps are also less intrinsically reliable than OEM mechanical pumps.
The mechanical fuel pump has a return line to the tank. Electric pumps don't. Whatever fuel the carb doesn't need, the excess fuel gets pumped by the mechanical pump back to the tank. There is a constant flow of gasoline flowing from the tank to the pump and back to the tank with the mechanical pump. The fuel going to the pump therefore can be cooler flowing to the carb on hot days because it spends less time in the hot engine compartment waiting to get pumped to the carb.
The return line feature of the mechanical pump can be beneficial for maintaining the fuel quality inside the gas tank too. When the engine isn't run that often and fuel isn't getting used up quickly, alcohol blended fuels will stratify into different density levels. With a mechanical pump always recirculating the fuel, this doesn't happen.
Bottom line:
Install the mechanical fuel pump and get rid of the electric one.
