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MG MGB Technical - SU Electronic Fuel Pump

I've been planning to change my '67 BGT from positive to negative ground. The plans did not include any deadline, so when it came time recently to order a new fuel pump, I ordered an SU that Moss said would work with either positive or negative ground. When I opened the box, I was surprised to find a piece of paper from SU stating that the pump, an AZX with black sealing tape, should be used only with negative ground.

This invited a deadline for the ground changeover, but now I'm curious as to whether the SU electronic pump might be a better choice. Anyone have experience with both the points-style pump and the electronic version? How do they compare? -G.
Glenn G

Glenn. Please be so kind as to visit my website at www.custompistols.com/ and view the tech articles by David DuBois. He did a great deal of research before writing the articles and honoring me by allowing me to post them. He contacted Burlen Fuel Systems, the current producer of the SU fuel pumps, to ensure that the information he provided was accurate. His e-mail address is hot linked in the first article, perhaps in the others. (My wife is the webmaster and what I do not know about computers would fill a very large book.)

Dave should be able to get you sorted as to what will work and what will not. I availled myself of his services and got back several very excellent rebuilt pumps which I am currently using.

Les
Les Bengtson

Fuel leaking from the carburetor is usually indicative that the needle and seat aren't sealing in the fuel bowl of the carburetor or the float is out of adjustment.
Kimberly

Glen - The first thing that I would do would be to get in contact with Moss and find out why they sent you a pump that is not what was advertized. It is possible that they were out of the non polarized pumps and sent you a polarized one rather than delay the shipment to you. If this is true, they should have told you what they were doing. I think that it is more likely that there was just contaminated stock or someone picked the wrong part, in which case Moss will make it good for you.

If you wind up being stuck with the negative ground pump, why not go ahead and convert the car to positive ground now instead of waiting. Other than the tach and any radio that may be installed, it is a simple process to convert to negative ground, taking no more than an hour. The tach (and radio if installed) can be left disconnected until a more convenient time to deal with them. If you don't have instructions on how to convert the car to negative ground, contact me at the above e-mail address and I'll send you instructions.

Finally, if push comes to shove, I can convert your pump to non polarized configuration if you want to ship it to me. An all electronic pump is definitely polarized son you wouldn't have anything to gain there. If you drive your car regularly, the points style pump will serve you well for many years (approx 100,000 miles). If you don't drive the car regularly, or lay it up for the winter, then an all electronic pump is the better choice as it doesn't have any points that will film over during long periods of disuse. Cheers - Dave
David DuBois

I put an electronic pump on my car which remains +ve ground for sentimental reasons. It must be 3 years now and so far so good.
Stan Best

I did call Moss about the pump they sent originally, and their "tech" person said that the pump could be connected to either positive or negative ground. He said to go ahead and install it and send it back if it failed. Easy for him to say, when I'd be the person twelve miles from home when it failed. I decided to exchange it for the negative-ground electronic pump, but then began to wonder if the electronic pump is overall better. It arrived today, and no one has mentioned any conclusive evidence that the electronic pumps are worse. I guess I'll go ahead and install it as soon as I carry out the conversion to negative ground. This is all a prelude to my plan to air-condition the car.

Will check out the Bengtson archives. I already have great respect for Mr. DuBois, as I was at wits' end trying to get air out of the clutch hydraulic system last year when I found his comment in the archives about pushing in the slave cylinder piston. Such a simple thing.

Thanks for the comments. -G.
Glenn G

Glen - I converted the pump on our MGB to all electronic, using the circuit from Burlen Fuel Systems about 5 years ago so that I could evaluate its operation. In that amount of time, the pump has not given us any problems at all (neither did the pump before this one that I had converted to solid state using my own circuit). Both circuits operate equally well, the only thing that I haven't determined yet is the life expectancy of each one (I'll let you know when they fail, if I live that long). Cheers - Dave
David DuBois

The 'X' pumps aren't electronic in terms of being 'pointless' but have a diode for points quenching in lieu of the original capacitor. It is quite easy to reverse the diode for the other polarity if needs be. Having said that using it unmodified on the 'other' polarity won't immediately harm anything as I understand the diode is protected against reverse polarity. However the pump will draw a bit more current when it operates, and the quenching won't be quite so effective meaning the points will fail sooner.

My V8 came with a fully electronic pump, which worked fine for quite a long time, then suddenly but intermittently started short-stroking and causing fuel starvation. Even though the electrics end is in the boot and I was able to observe the bits while it was happening I could not make it happen when it wasn't or stop it when it was, it just made its own mind up. After two or three bouts of this (and the consequent stranding) I fitted a refurbished points-type pump and have had no more problems to date. I have to say that I would *never* fit a fully electronic pump by choice, the points type are usually 'fixable' by the roadside, often with a judicious thump which will get you home, and is an advance warning to clean and reset the points.
Paul Hunt 2

To add to what Paul stated regarding the diode quenching unit, the unit is a diode with a series resistor in a single package. Reversing the polarity on the pump, without reversing the diode/resistor unit will as Paul states, not cause any immediate damage, but it will cause excessive arcing of the points and will greatly shorten the life of them. I believe that in hte past year, Burlen Fuel Systems has started using a bi-directional Transient Voltage Suppressor (TVS) in place of the diode/resistor arc suppressor, which makes the points style pumps, once again non polarized. Cheers - Dave
David DuBois

This thread was discussed between 11/10/2006 and 13/10/2006

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