eagle freak is correct. Pick one or the other. Don't put pressure on the backside of the mechanical pump. Not only is there a possibility of the diaphragm rupturing and filling the crank case with fuel or spraying fuel out the vent and all over your engine, engine compartment, and the ground, but you may just defeat the mechanical pumps spring, filling the pumping chamber with fuel keeping the diaphragm from being lifted by the pump lever. in essence bypassing the mechanical pumps ability to pump. The spring under the diaphragm is actually what is pushing the fuel to the carb. The pump levers only job is to compress that spring pulling the fuel into the chamber. then the spring pushes that fuel toward the carb as needed.
Also, the pressure on the backside may cause the check-valve in the mechanical pump to remain open or not fully seat defeating the springs ability to push the fuel to the carb, pushing fuel in 2 directions, back against the electric pump and up to the carb.
If you are having problems with the mechanical pump, look for the reason why. Is the pump bad? is the pickup in the tank plugged up? Is the fuel filter plugged up? do you have a crushed fuel line? Is the carb starving for fuel: is the float set correctly, or is the float valve sticking closed? If the mechanical pump is good and you still have problems, you could install the electric pump and still have the same problems.
If you install the electric pump, make sure it is as close to the fuel source as possible because it is designed to push fuel not pull it.
In a diesel many times you will have a lift pump and then the main pump to the injectors. But system is designed that way.
Topic: Electric fuel pump specs (Read 4308 times)