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MG MGB Technical - Fuel Pump Runs Continously

I have a 1979 MGB that has an aftermarket electric fuel pump.... looks like a cylinder about 6-8" long. As soon as I turn the key on it starts running and never shuts off. I first thought it might be pumping gas through the needle with too much pressure. But I disconnected the incoming fuel line at the carb and plugged it. The pump continued to run and run and run. Do you think I need to replace the pump or is there some cut off switch that needs replaced? Thanks.
Lee Gooch

I can't tell how your pump is meant to work, but the normal SU pump is switched off by the back pressure once the float chamber on the carb(s) are full. There is no other switching mechanism.
Mike Howlett

Most aftermarket pumps do run continuously. They are not positive displacement pumps, so there is no problem with that.
David "I don't remember the last functional SU pump I had" Lieb
David Lieb

My after market also runs all the time. It's normal for many after market pumps.

Clifton Gordon

If your aftermarket is electronic, it will most likely run continuously. Rubber buffering mounts will help ease the pain in your ears somewhat.
rick ingram

How many non-SU fuel pumps useable on an MG do NOT run continuously? None of my six Spridgets came with a functional SU pump. All of them run continuously. For that matter, even the mechanical ones "run continuously" ;-). If using the cubist Facet pumps, a transmission mount from an MGB can isolate it nicely, too.
David "someday I will own a functional SU pump..." Lieb
David Lieb

My Hardi fuel pump is demand triggered like an SU. I don't think you can buy these in the states anymore. It has been reliable for at least 15 years and 70k miles. I imagine it has points but as far as I know you cannot service them if you wanted to.

Robert McCoy

It is probably a rollervane pump. These run all the time.

As implied by the name, these have vanes and the thing rotates continuously. Usually rollervane pumps are high pressure EFI pumps, however there are also low pressure roller vane pumps. I have one on my car. A universal auto suction pump made by peirberg. It looks a bit like a small spark plug coil. I have done over 50,000 using this pump and have no problems with it.
It should not be noisy, a low pitched humming noise that is not audible when the motor is running. Assaid above, it should be mounted on rubber. An old engine mount works well. If it is buzzing loudly it is cavitating (pulling air).
Many people swear by the SU fuel pump,
I tend to swear AT them.
The SU fuel pump has given me some very unpleasant experiences.
Peter Sherman

The pump off a 82 SUBARU (and Honda Civic, and probably a few other cars and years) works well and has that click-ity-click noise common to all on demand reciprocating pumps like SU's. This was reliable and did not overflow the carbies when I was using it on the old 1800 motor.
Peter Sherman

Thanks everyone for the feedback. I guess I just hadn't noticed the continuous running before. I'll try the rubber cushion approach and not worry about it running.
Lee Gooch

This thread was discussed between 11/03/2008 and 12/03/2008

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