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MG MGA - Electronic SU fuel pump - Moss type?

Hi Guys,

I'm in need of a new electronic (solid state) SU fuel pump. These come in either positve or negative earth:

But the SU fuel pump that moss sells is not polarity sensitive:

Can someone please shed some light on the moss model. Is it a points/capacitor type of SU pump (not polarity sensitive)?

Thanks for the help guys.
B Rollo

The polarity-sensitive units have a diode for arc suppression. Non-polarity-sensitive units have a capacitor for arc suppression. I had a go-round with one of these last April because it would run for no more than a few minutes at a time, then quit. It turned out to be a mechanical problem with the contact points mechanism, not the capacitor.

See pictures here:
The light blue disc with white wires is the capacitor. I was amazed at the small size of this capacitor. In decades past I was familiar with capacitor type pumps where the capacitor was much larger, being a small metal barrel similar to an ignition condenser. I have no grounds to believe this capacitor won't work, but it just looks funny to me. Original MGA fuel pumps worked well for a substantial life with no capacitor, but were subject to a little burning of the points over time.

This mechanical problem was reported to Moss in April. I do not know if this is an single isolated case or a generic problem with a production batch. I have no more response from Moss since they said they would refer it to the manufacture (Burlen) for consideration, so I wouldn't recommend this one to anyone. My friend got tired of waiting for a response and recently bought an aftermarket fuel pump to get his daily driver MGA back on the road.
Barney Gaylord

For what it is worth, I have been using one from Moss for two years and am quite happy with it. Looks original, sounds originl, and operates great! My car is a neg ground.
WMR Bill

I have not had the best experiance with the newer SU pumps. One pump had the diode and burned the points up at about 18,000 miles. A second one on my other car just torched the points in 3,000 miles. The second one has the small blue disk shown in Barney's picture. The small blue disk is not a capacitor, it is a metal oxide varister, MOV for short. MOV's act like a diode but are not polarity sensitive. They have a voltage rating at which they will conduct, clamping the circut when the voltage spike exceeds there design value. While the capacitor can store energy and act somewhat like a shock absorber to the voltage generated when the points open, the diode and MOV do not, they look like a short circut. The first pump had it,s points replaced and a capacitor installed from the pump it replaced, so far no problems. The second one will get new points and a capacitor. While in theory the diode or MOV should work it doesn't seem too. Since they built the old pumps with capacitors for decades with no problems it seems to me this change was a method of saving a few cents. If the diode or MOV's worked so well you would have them in your dizzy instead of the capacitor.
J Heisenfeldt

Thank you JH. Learn something new every day. I knew about MOV (metal oxide varistor), just didn't catch the association to this application. Mental block I suppose. If the MOV is breaking down in service, it may be too small for the application, or possibly defective parts. For those who don't know what a varistor is, check here:

Our problem with this particular fuel pump was not the varistor, but was a mechanical problem with the contact points alignment. A little nudge to the points would make it run for a short time before it would stop again. As far as I know the problem has not been resolved, or has not been determined to be a single bad part or a problem with a production batch.

The typical modus operandi for Moss is to continue to sell the parts as long as there are not excessive returns. If you have one that works, don't scoff. If you have one that gives you trouble, definitely notify the vendor.
Barney Gaylord

The all electronic pumps that Moss sells is in fact electronic, not just a diode to protect the points. These pumps are polarity sensitive due to the Hall effect circuit (the polarity can be changed quite easily by someone with knowledge of electronics). The pumps that Moss sells that are not polarity sensitive are a points style pump that has the MOV for arc suppression. There is a third alternative available, Tony Oliver in Australia now repairs the pumps and can convert them to solid state (using an optical trigger). Tony's e-mail address is:
Cheers - Dave
David DuBois

Thanks for all that information and your personal experiences with some of these SU pumps. I understand the differences between the two 'new' SU pumps now. It sounds as if one would be taking a slight risk with the new points type SU pump (as per Barney's example). Perhaps the all electronic SU model or repair of my existing pump (thanks for that information David) is the best bet. Cheers guys.
B Rollo

Or you can buy an electronic module direct from Burlen to fit into an original points style pump
dominic clancy

This thread was discussed between 03/09/2008 and 04/09/2008

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