Can A Mechanical Pump Pull Fuel Through A Non-running Electric Pump.

A while ago, my electric pump clogged up on me and stopped all fuel flow. 2 hours and lots of gas inhaled later, I decided I'd go ahead and re-do the fuel delivery system.

I have dual tanks on my CJ with no return lines plumbed in. My pump has a spot for a return line which I will use. I will have both tanks run to a valve, and from there they will run to the mechanical pump.
My question is this: If I put an electric pump after the valve and before the mechanical pump, can the mechanical pump pull fuel through the electrical pump without hurting either pump?

My point in all this is that I would like to have an electric pump for priming and use as a backup if my mechanical pump fails, but I doubt that I will remember to turn it on.'


Here's the simplified version of my scenario:

tank - fuel valve - electric pump - fuel line - mechanical pump - regulator - carb

 

In general yes, commonly done. Carburetors only need 3-5 psi.

 

Depends on the electric pump. The little low pressure rattle cubes are perfect and have check valves to not fill from the other tank. The bigger gear pumps won't free flow.

 

I have a couple of cheapo Summit pumps on order. One will sit on the engine-side of the tank selector valve, not the tank side. The other will be a spare.

 

Be aware In that case your "both" selection on the valve will allow your front tank to fill your rear tank when parked. You must have all your fillers and vents above the fuel level of the highest tank.

 

I'll keep that in mind. Thanks.

 

It depends on the type of pump. Just about all the diaphragm pumps will allow fuel to be sucked through them. The gear pumps, not so much.

 

I tried that on my CJ5. Put an electric pump back by the tank with a push button to fill the carb after it sits. It would idle and run at slow speeds but seemed to get starved for fuel as RPM's increased. Then the engine would die. It must have been a restrictive electric pump because the Jeep had one on it when I bought and it and it worked fine. I replaced it when I restored the Jeep, should have left it alone!

 

I have done this setup, my electric fuel pump does not flow when not powered, in either direction. So I come out of the tank and I installed a TEE. one line goes to the mech fuel pump the other line goes to the electric. the output of the electric goes up front to the output of the mechanical and tee into the line going to the carb. Also make sure the fuel filter with return line has a restrictor in place. The cheap ones do not and this will cause all types of fuel starvation issues.

I don't know why the fuel drains back into the tank, but it does. My Jeep only has to sit 24 hours and no fuel will be in the lines. So I turn on the dash sw, wait 10 - 15 sec, pump twice and start.

 

I've read that you can make a simple pump bypass with a one-way valve around the electric pump, and I'll go that way if I have problems with my clackity-Summit pump.


[ _ = fuel lines | -> = direction of flow | T = t-fitting/split | . = nothing (spacing problem with graph)]

(tank)->_ _(electric pump)->__ __->(mechanical pump)
..............T_(one way valve)->_T