Why A Mechanical and Electric Fuel Pump Together?

[boboh1]

Working on the Coronet and noticed an on/off switch in the glove box. Followed the wire to the rear of the car to discover an electric fuel pump. But a mechanical one is also installed so why would it be necessary for the previous owner to also put this pump in too?

 

[HD539]

I installed the electric fuel pump to prime the carburetor. if the car has sat for awhile I turn the electric fuel pump on for a few seconds, starts a lot easier.

 

[j-c-c-62]

It would also help with the 50-60's dreaded vapor lock I suspect

 

[496 polara]

Maybe as a booster pump under heavy demand if the stock pump couldn't keep up under load.

 

[snakeoil24]

Use electric to fill bowls then turn right off, that will avoid bursting diaphragm in mechanical which will fill crank case with raw gas

 

[Fran Blacker]

If that electric pump is a Carter and you shut it off the mechanical pump won't draw through it. Had a wire fall off mine and carbs ran dry.

 

[boboh1]

Makes a bit more sense with these good answers. It is not a Carter pump so I think the car still ran with it shut off. It looks really old so will probably end up removing it and putting everything back to stock.

 

[33 IMP]

Welcome new member, from fellow Claremont resident.

 

[boboh1]

Thanks very much. Taxifornia. LOL

 

[RemCharger]

I put one on to help me sleep with a 125 shot on it lol.
Everything survived

 

[Geoff 2]

That IS a Carter elec pump [ or Federal Mogul who bought Carter ]. But Carter design, lasts forever. I would ditch the mech pump & just use the elec pump. Mech pumps are NOT designed to pull through other pumps....

 

[snakeoil24]

That IS a Carter elec pump [ or Federal Mogul who bought Carter ]. But Carter design, lasts forever. I would ditch the mech pump & just use the elec pump. Mech pumps are NOT designed to pull through other pumps....

You .mean push thru from other pumps

 

[Davefinan]

If that electric pump is a Carter and you shut it off the mechanical pump won't draw through it. Had a wire fall off mine and carbs ran dry.

Makes sense to me

 

[451Mopar]

usually to prime mechanical pump and carb, but really just twice as many things to go wrong.

 

[Geoff 2]

Post#12. No, pull through other pumps.

 

[lewtot184]

Makes a bit more sense with these good answers. It is not a Carter pump so I think the car still ran with it shut off. It looks really old so will probably end up removing it and putting everything back to stock.

are you sure that's not a carter pump?

 

[MCODECUDA]

I started building a fuel system with two pickups in the tank. One system was mechanical with an adjustable fuel pressure switch. When the pressure would drop to a certain point the switch would turn on the electric pump. It was pretty trick in that I had a duel feed top for my AVS and the second line ran behind the motor.

 

[Dodge Bros]

I have had great luck with systems like that. Carter sells a check valve set up that lets the mechanical pump bypass the electric pump when it is shut off. I run one. The mechanical pump will also pull thru some electric pumps with almost no restrictions with the electric pump shut off. Have one of them also. Holley’s street pump (and knock offs) do not need the check valve set up. The chatter pumps do not seem to need the check valve bypass either.

I know of a 3800 lb car running in the 9s with a tandem mechanical pump and holley street pump in series with 3/8” line. When the pumps are ran in series it improves each pumps performance, less line loss or head loss. Moving each pump too the top of it’s performance curve. I use it to prime the carb, then for full throttle stuff I leave it on. We have a couple tanks systems with intake electrics, and have cars with a sump with a electric pump. With B bodies long tanks it seems like the baffled tanks system is hard to beat if your quick off the line. But honestly, the tandem set up works really good. Espically on the later b bodies with shorter fuel tanks. Works outstanding on an A body. Fwiw

 

[boboh1]

are you sure that's not a carter pump?

After I removed it and had a better look at it, turns out it was indeed a Carter pump.

 

[Dodge Bros]

If it is already wired up I would absolute leave it and run both. Get a check valve system to bypass like the pic, add a electric switch to turn in off separately. Then you have a back up when the mechanical pump craps out, don’t have to run it if you don’t need it, but you can prime the engine after it sits for quick starts or vapor lock protection. Plus you have more fuel flow running both..if you need it. Any one of those reasons is good enough to keep it. Quality on mechanical fuel pumps now is terrible, mechanical pumps do not last like they use to.