Re: ELECTRIC FUEL PUMP

Posted by DavidPackard On 2020/1/13 16:11:54

My two cents worth.

When I bought my '48 it was equipped with a Carter, rear mounted, electric pump. It was mounted on the sheet metal behind the left rear wheel easily visible with the 'fuel filler' door open. It was hooked up without a by-pass circuit and attendant check valve. Because the engine was equipped with a mechanical pump, I thought the previous owner had installed the pump to overcome fuel evaporation during a period of storage in sunny Arizona. The mechanical pump would then be expected to 'draw' fuel through the pump whether it was powered, or not. My '54 is similarly equipped, but the pump is an 'Airtex' mounted on the left frame rail. That car is equally equipped with an engine mounted mechanical pump, so the 'draw through' expectation would also apply.

Now for the rest of the story:

I treated both installations equally, that is, I would run the E-pump for a few seconds prior to a 'wake-up from hibernation' start, and then shut-off the E-pump, and drive the car normally thereafter. The flaw was treating the installations as being equal, they were most assuredly not. The Airtex fule pump ('54) is a pulsating solenoid design that represents very little restriction when the power is removed (there is an integral fuel filter of unknown restriction). The '54 has never exhibited a fuel delivery problem. The Carter fuel pump ('48) is a rotary vane design who's restriction is quite unpredictable. If the vanes park in their slots there is little or no restriction. If the vanes however park further out of their slots some amount of restriction will occur . . . .including enough restriction to completely inhibit flow. The net result was unpredictable lack of power, sputtering, and stalling . . . all of which was quite curable by turning on the E-pump. Worst yet road vibration can promote a vane to walk towards a maximum restriction position, so the sputtering and stalling could strike at any time during the drive.

Over a year ago, I 'deep-sixed' the Carter pump and installed an Airtex model E8011. The Airtex installation is now on the left frame rail just forward of the rear wheel, and is without a by-pass circuit. The symptoms of sputtering, and stalling have not reoccurred since the pump change. While trouble-shooting the Carter equipped system I installed an electric fuel pressure gauge (readable while the car was moving), and that confirmed that at times the fuel pressure would be zero when equipped with the Carter pump un-powered. That gauge also confirmed the fuel pressure after the pump change was approximately 3 psi then the car was underway, Airtex E-pump OFF, and not over 4 psi when the Airtex E-pump has ON. With a completely dry WDO carburetor it took approximately 10 seconds to achieve 3 - 4 psi. The pressure was a few psi lower while the carburetor was filling.

I've concluded from my experience that if the engine is equipped with a mechanical fuel pump an Airtex E8011 (also assumes a six volt installation), without a by-pass circuit, is suitable for carburetor priming purposes. That configuration will not require power once the carburetor is 'primed'. To expand on West Peterson's observation, I believe the initial location of fuel vaporization is the inlet fitting of the mechanical pump, or inside the mechanical pump's strainer cup. If the E-pump is not powered (Airtex only) I do not believe the pressure at this (these) location(s) will be any different whether the E-pump is mounted in the rear, or up forward, therefore 'vapor lock' is not likely influenced by the location of the E-pump. With respect to the by-pass circuit; if a regulator is not included, as supported by West Peterson, then what we have is a parallel flow circuit one with the pressure drop of an un-running E-pump, and the other the pressure drop of a check valve. Most of the automotive check valves I've seen use a spring loaded 'ball check' that will unseat at a particular pressure, mostly 2 psid, but others are also available. This pressure will essentially become the pressure drop of the device for most of the flow range. I believe an un-running Airtex E-pump will have less pressure drop than a check valve of this design. This leads to most, if not all, of the fuel flow will be through the E-pump, and little if any through the check valve. All of this applies to the Airtex design only. In the case of the Carter design, the by-pass circuit is required if the E-pump will be un-powered after the priming process. The pressure loss of the check valve will still apply, and this pressure drop will persist throughout the remainder of the suction side of the fuel delivery circuit whenever the rotary vanes are restricting the fuel flow.

My experience suggests an Airtex E8011 (assumes six volt application) can be used powered or unpowered without over pressurizing the carburetor inlet valve, therefore a pressure regulator is not required. And if a regulator is not included the entire by-pass loop is also not needed.

WauhopM, if your car is six volt, I suggest an Airtex E8011 fuel pump, mounted either forward or aft, powered by a momentary switch, and plumbed without a by-pass circuit. Instruction that come with the E-pump suggest the pump be mounted 'nose high', by just a little bit, to purge air out of the body of the pump.

dp