Electric fuel pump question

MOTORHEAD · #1 (**permalink**) 10-06-2017, 01:30 PM

My Kirkham, built in 1998, was equipt with an electric fuel pump and filter in the trunk, as per the original S/C's. It also had an engine driven pump. When I rebuilt the car, I set it up the same way, however I could never pump any fuel with the electric pump on or off. (yes the pump had been checked). I chalked it up to the electric pump being in the trunk, higher than the tank ( the original cars had Bendix "plunger" pumps, which would pull a vacumn , and would work in that situation) So I bypassed the pump, and have been running on the engine pump without a problem.
Now I'm moving the battery to the trunk so I need to get the fuel components out of there, Electric pump will go under the car, and will be lower than the tank, so feeding it won't be a problem, but I need to know if the engine pump will pull fuel thru the electric pump when it is shut off ?

Ted

Riverside racer · #2 (**permalink**) 10-06-2017, 05:07 PM

Yes it will. I use both with the electric as standby... I switch on for starting with 48 IDA`S then turn off and that works well.
Ross

Ron61 · #3 (**permalink**) 10-07-2017, 03:30 AM

Mine worked well as Riverside racer said. I had it mounted on the frame just below the tank and when I turned it off the mechanical pump worked just fine. I never ran it when racing though without both of them going so I am not sure if the electric pump would have put enough choke in the line to slow the gas down at high RPM just using the mechanical pump.

Ron

MOTORHEAD · #4 (**permalink**) 10-07-2017, 06:29 AM

Thanks Guys, that's what I thought. I wanted to make sure before I mounted everything.
I made the mistake of calling Holley tech. He said that fuel wouldn't flow with the pump shut off, I asked "is it a "positive displacement" pump?" He says "what's that ?" .

Phx Mike · #5 (**permalink**) 10-07-2017, 07:07 AM

For what it's worth on mine I have the Holley Red electric pump mounted on the frame rail just below the tank. With the electric running I get a steady 5 psi fuel pressure but if I shut it off and run just on the mechanical it drops to 2-3 psi which is too low in my view. I do think the electric pump, when shut off, creates quite a bit of suction side restriction for the mechanical pump. Maybe just on mine and others may have had different experiences.

MOTORHEAD · #6 (**permalink**) 05-17-2018, 06:18 AM

Thought I would update this thread with a little new info; the mechanical fuel pump Will pull fuel through the electric pump with the electric pump shut off. Drove the car around town, and all was well. Then I was driving on the hiway, about 70 mph, and the engine started to cut out ! I though " uh-oh, what now !, but then I remembered the elect. pump, turned it on, and all was well again ! So the electric pump does restrict the flow when it's not running, in my case at about 70mph, your results may vary.
Also, it's very handy to use to set the fuel bowl levels without having to run the engine .-

HI Cobra · #7 (**permalink**) 05-17-2018, 07:04 PM

I have the electric fuel pump above my tank, rt hand side on the Kirkham.
I get about 7psi with it on and 4 - 6 with it off. I have had fuel starvation with just the mechanical at higher speeds too, which reminds me to turn it on.

I added an electric fuel pump to my Classic Roadster years ago to prime it if I
hadn't run it for awhile. It would take forever for the mechanical to bring it forward. Now if I haven't run it for awhile I let it turn over until I get oil pressure,
then stop and turn on the electric pump and listen for it to slow down when it
gets pressure (it stops - cheap kind). Then I just pump the gas once and it starts right up. I also do the same basically with the Kirkham, to pre-oil it.

So far so good with that strategy. Priming the CR was a big help. Both electric fuel pumps are toggle switch operated.

MOTORHEAD · #8 (**permalink**) 05-18-2018, 06:25 AM

Flip: Was the pump on your Kirkham the red Holley, installed by Kirkham when the car was built?

Ted

HI Cobra · #9 (**permalink**) 05-18-2018, 10:06 AM

Ted,
I did not put the car together but did recently replace the existing fuel pump, which was a Mallory 110 gph 4110. I guess they got bought out by MSD but the
new pump is the same except the new part number is 29256. I took the old one
apart and found the brushes were gone so got some more and it works fine so I have it as a back-up. No change in the plumbing. Hope that helps.

BAsque1 · #10 (**permalink**) 05-23-2018, 04:29 AM

I am glad someone is talking fuel pressure, I have one properly connected in my car below the tank, never removed the mechanical. Had a huge problem with the electric one that cannot be adjusted below 9 lbs hence damaged my carb, had to replace the carb and I needed to disconnect the fuel pump and go back to the mechanical with the recommended 5lbs of pressure. All is well now.

Ron61 · #11 (**permalink**) 05-23-2018, 05:57 AM

Lou,

I ran a Holly Racing electric fuel pump in my other car that put out up to 18 pounds of pressure, but I got an inline pressure gauge and adjusting setup that worked great all the years I had the car. I could adjust it from 3 to 10 pounds so I ran it at the recommended 6 pounds. The gauge was right on the adjusting setup so you could watch it as you adjusted the pressure.

Ron

tortuga · #12 (**permalink**) 05-27-2018, 06:04 AM

Parallel with check valves?

MOTORHEAD · #13 (**permalink**) 05-27-2018, 08:02 AM

Tortuga: which post are you referring to?

spdbrake · #14 (**permalink**) 05-27-2018, 09:11 AM

I'm guessing he means, installing t-fittings on both sides of the Elec pump and again at the Mech pump. Then install a short bypass line with a Check valve to each T-fitting. Ensuring the flow arrows point to the Carb.
That way neither pump has to suck or push thru the failed unit and the Check valves will prevent reverse flow back to the tank.