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MG MGB Technical - Standby Fuel Pump

I bought a Carter inline fuel pump (the kind with a fuel filter before the inlet side) to use as a standby fuel pump on my 73 MGB.

Question: Can I remove the gas filter in my engine bay and install the Carter pump w/filter in that location or does the Carter have to be in the back of the car near the tank? Thank you.
David B

Some pumps are better at blowing than sucking. Near the back it has to do very little sucking, near the front quite a bit.
Paul Hunt 2

Hi David

I have a Carter fuel pump as well 'Carter Performance Electric Fuel Pump P4594 7ps' which I installed when I did my V8 conversion.
I installed the Carter in the same location as my 74.5 (bolted to the trunk, just behind the battery). I did run 2 filters for short period of time to ensure that no foreign particles had been missed. Now I just have one in-line before the pump. If I remember correctly the installation instructions say the filter should be before the pump.
I am not sure what PSI your Carter pump is but have you checked into whether or not you need a fuel pressure regulator?


Bruce
Bruce Mills

David - See my article on permanently installed back up fuel pumps at: http://www.custompistols.com/cars/dave/BackUpFuelPump.htm
I believe that the rational for installing the pumps near the fuel tank rather than in the engine compartment is that the inlet side of the pump is always at a lower pressure (vacuum) and is more prone to vapor lock if it is located in the hot engine comparement. By locating the pump near the tank, the fuel lines are always pressurized and thus are less inclined to form a vapor lock. That said, I am not sure that this is a real problem but rather something to keep inthe back pf your mind if you do develop a problem in that regard. My article includes the part numbers for various after market pumps that are good to use as back up pumps. The main thing is that teh pump is an all electronic pump (both the Facet and the Carter pumps are) so that there are no points in the pump to film over during long periods of disuse. It is also a good idea to check the pump periodically to insure that it is still working. The myth of "pusher vs puller" pumps is one that I have trying to dispell for some time (sorry Paul). At least as far as the SU fuel pump are concerned, all of them, low pressure and high perssure pumps develop about the same amount of inlet vacuum when they are running (as measured with a standard vacuum gauge) and all are quite capable of pulling fuel from the tank to the heigth of the engine compartment (and much further). That leaves all SU fuel pump being pushers, with the high pressure pumps pushing harder than the low pressure pumps (due to the volute spring used). The only consideration is that the low pressure pump would not be used back by the tank due to the drop in the already low pressure (maximum of 1.5 PSI) which would leave little pressure available at the float bowl. The high pressure pumps can be used in either location. Cheers - Dave
David DuBois

David
if you run the pumps in series - the Carter mounted in the engine bay will at least get you home. If you mount it by the tank - there is a chance the weather will get to it before you need it. The key point is that when the SU fails, it is possible for the Carter to suck fuel past the pump mechanism.

However, it is wise to have a fuel filter both before the pump and at the end of the fuel line before the carbs - one protects the pump, the second protects the carbs.

The pumps have been my sole reason for breakdown over many years of MG motoring.

Roger
RMW

Roger - I am not all that familiar with the Carter pumps and was not aware that they are vulnerable to the weather. The back up pump I installed in our MGB is a Facet, mounted on the back side of the right hand battery box and I have not had any problem with deterioration in the 3 years that it has been installed (our MGB is driven daily year around). The Carter may be a different situation.

I do no advocate (and in fact discourage) modern filters between the tank and a SU fuel pump, particularly the later ones. The reason for this stance is that modern paper filters can become so full of fine rust particles that they will no longer pass fuel. If/when this happens the SU fuel pump will stall in a current on condition and if the power is left of for any period of time, it will burn out the internal swamping resistor, resulting in rapid deterioration of the points due to excessive arcing. Worse, since the swamping resistor is contained inside the coil housing and out of sigh, one doesn't know that it is burned out and upon replacing the points, will find that the new points will last only a short time before they too, are burned beyond use. The SU fuel pumps have a course filter on the inlet side that will keep out any big chunks that might harm the pump. Anything smaller will pas on through the pump and into he float bowl of the carburetor, where they setle out to the bottom. If one feels the need for additional filtering of the fuel, place the filter after the pump, where a clog will stall the pump in a current off condition where there will be no damage caused to the pump. Cheers - Dave
David DuBois

David,

I have used the Carter fuel pump for over 15 years in my MGB. I don't even use it as a back up. Mine has never failed me. The Carter comes with the filter installed already before the pump to keep the pump clean.

I also have a supercharger on my car with another clear type fuel filter before the carburetor. I have a pressure regulator before the filter set at 3 psi. At WOT I never had any problem with lack of fuel.

Two fuel filters to me is better than one, and if I can use it with a supercharger I am sure you can.

Ray
Ray 1977mgb

A French ship-designer who had attended a presentation a few years back observed that the design which we had just heard about was well ahead of the French. I suggested that their designers might pick up on certain aspects.

There was a pause and he replied " maybe, but we prefer to learn from our own experience"

Petrol occasionally comes with unexpected additives.

FWIW

Roger
RMW

Hi folks,

Two-pennyworth of thoughts regarding standby fuel pumps and reserve fuel tanks.

If you were to run another fuel line into the tank and terminate it, say, half an inch (1cm) above the existing fuel pick up point and take the new line to the existing pump the pump will cease pumping with a reserve of fuel left in the tank. Another, electric, pump can provide the remaining fuel when required. Obviously a T-piece to join the fuel pipes before running to the engine is required.

This concept came from a 1500 midget which could benefit from an electric pump to prime the carburrettors on a hot day before the mechanical pump operates.

In either case, if the original pump fails the back up is available at the throw of a switch or transfer of a Lucar connector. Come to think of it, a 3-position, centre-off switch could provide a simple, if primitive, anti-theft device.

FWIW

Peter
P L Hills

This thread was discussed between 21/05/2006 and 25/05/2006

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