Carter electric fuel pump 4070

[nismou20]

So do external electric fuel pumps just start failing over time like other in tank pumps? Other than the motor just crapping out my fuel pressure seems to be going down over time now. At 10 years It’s been good to me but I’ve been having to increase the pressure slightly ever so often when engine starts to stumble off idle.

While discussing these low pressure Hi volume pumps Carter claims these to be self internally regulating at 4-6 psi. I’ve been regulating the pressure with a micro regulator down to 3.5 psi. How could these pumps even regulate the pressure internally?

[GeoffM]

OK so your pump is a rotary lobe style pump. The pump has a rotor attached to the electric motor that rotates inside the round pump casing. The rotor looks like a swastika and in each 4 pockets of the swastika there is a rubber vane that acts like a sweeper and seals to the outside casing, forming a pocket. When the lobes rotate, fuel enters into a pocket that is created by the vanes and gets carried around to the discharge port. It's basically like a gear pump but with rubber vanes creating a pocket to transfer the fuel from suction to discharge instead of gears. The "internal pressure regulation" is simply the capacity for the rubber vanes to resist the back-pressure. If there is too much back-pressure (not enough fuel demand), the pressure gets so high that it deflects the rubber vanes and therefore relieves back to the next pocket in the lobe. ( as opposed to an oil pump which has metal gears so it needs a spring loaded ball-check valve to relieve excess pressure)

A rotary lobe pump relies on the seal between the rubber vane and the pump casing to achieve it's ability to pump it's volume vs. the system back-pressure. As the rubber wears over time or gets attacked by chemicals and gets spongy, the amount of internal relief increases because the seal to each pocket gets weaker so it cant hold the same pressure without relieving. (on a diaphragm fuel pump, it's the check valve seats that takes the wear and limits the pumps life). You'll see lower pressure at the carb regulator for a given volume demand.
So, 10 years of rubbin' might mean the end of service life for the little rubber bits.

[nismou20]

Thankyou for that! Well explained that even I can understand. I guess it’s time to hunt down another pump.

[2mAn]

Can you post some pics of your setup? I want to convert mine to an electric pump eventually

[nismou20]

Mine just mounts off a bracket that’s bolted to the frame by the steering idler. (Very crude) it should be used as a pusher I know but it’s worked fine as a puller. Space is limited and I didn’t want to bother mounting under the car by fuel tank if it crapped out on a run. Easier access for me. The kit comes with bracket, 3 bolts and rubber isolaters for vibration but mine is just suspended by one.

[redroadster]

Do you wire a relay off the alt to it ?
or just the ign. on

[nismou20]

So, I bypassed the regulator and found the pressure would peg to max which was 5psi on my gauge. Noting that Carter pump was good reinstalled reg and set to 3.5. Still kept getting a miss that was driving me crazy. Finally pulled the dist cap and all four terminals had this heavy coating of carbon that was acting like a insulator. Flaked it off and now no miss! Guess it’s price I pay for the MSD 6AL and I had just rebuilt this motor earlier in the year.

[jhayden]

Interesting ... I have had MSD6 on both our U20 and a Volvo B30 (inboard w/triple Solexes) for over 25 years w/o any such problem, or any other ignition problems, for that matter.

Both also have the MSD coil. Did you also opt for that as well?

Jon

[fj20spl311]

I have had several of these pumps for years. @GeoffM is correct about the basic design, but I have never seen any rubber part inside the pump. It uses 4 polished metal squares that seal because of the centrifugal force. Its a very cleaver design, with all metal parts except the shaft seal and gasket.
I suspect the pressure regulation is in the design. If the flow is so low that the pressure builds, the RPM of the pump would also slow and the centrifugal force on the metal squares is reduced and the seal is less allowing the fuel pump to flow less volume which reduces the pressure.

[fj20spl311]

So, I bypassed the regulator and found the pressure would peg to max which was 5psi on my gauge. Noting that Carter pump was good reinstalled reg and set to 3.5. Still kept getting a miss that was driving me crazy. Finally pulled the dist cap and all four terminals had this heavy coating of carbon that was acting like a insulator. Flaked it off and now no miss! Guess it’s price I pay for the MSD 6AL and I had just rebuilt this motor earlier in the year.

Should have asked LINDA, I am pretty sure she has been fights that same MSD 6AL "problem"

[nismou20]

Yes EI distributor and MSD + Blaster 2 coil. These eat up MSD sparkplug terminals too. When I took dist cap off there was a thin sheet of carbon build on every cap terminal that I peeled away.

[Linda]

Tom
This hot rod , race car builder guru guy at SCS told me to drill 2 holes in the cap, 1 ea between 2 terminals at the rotor level. It vents the cap to reduce or eliminate the carbon build up gases, or something like that. lol. Seems to be working.
Also be sure the MSD connection is good, and the coil wire is good. Mine was weak at the coil so I redid it with a new MSD terminal.
Brass distributor caps best, but have used aluminum too.
I used a Dremel with a brass brush, (Harbor Freight set) to lightly buzz off the carbon, then a wipe with a 400 grit sandpaper. You can do this a time or 2 without taking off too much, but then you need a new cap. A quick wipe on the rotor too, which can also carbon up a bit.
Linda

[nismou20]

I just read that about ionization within the cap that can cause this. And yeah it was suggested drilling holes about 1/4 inch ones between the rotor terminals. Weird stuff!

[jhayden]

Again, all this is news to me. No problems, so there was no need to investigate! Well over 25 years in both applications, but both still retain points rather than EI to trigger the MSD. Points only wear on the rubbing block rather than burn (same as old motorcycles) with the MSD, so very rarely need replacement. The points also deliver 7K rpm w/o float on the U20, so that is adequate.

Although the Volvo application has endured some pretty severe conditions in a marine environment, it has never had a hiccup. Both it and the U20 have precut wires (not "custom fitted" by the owner), and both have factory cap and rotor: Nissan for the U20, and Bosch for the B30.

Maybe just lucky, but now very thankful not to have experienced your gremlins.

Jon

[GeoffM]

I have had several of these pumps for years. @GeoffM is correct about the basic design, but I have never seen any rubber part inside the pump. It uses 4 polished metal squares that seal because of the centrifugal force. Its a very cleaver design, with all metal parts except the shaft seal and gasket.
I suspect the pressure regulation is in the design. If the flow is so low that the pressure builds, the RPM of the pump would also slow and the centrifugal force on the metal squares is reduced and the seal is less allowing the fuel pump to flow less volume which reduces the pressure.

Ah, thanks for the correction. I assumed it was the rubber vane type. The metal vane type works very similarly except the vane slides in the pocket of the hub. Except the back-pressure shouldn't change the speed of the motor (that's not how electric motors work unless there is a VFD on the pump which I doubt). As you say the excess back-pressure forces the vane away from the casing letting the pressure bypass.