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MG MGB Technical - Fuel Pump Compatibility

I've been away for a little while; but now I've returned with much to post about. My pressing issue of the moment has to do with my fuel pump.

For those of you who don't want to read the whole story of how I came to this issue (included below), here are my questions:

I currently have a negative ground AUF 300 Series SU fuel pump in my 1974.5 MGB with twin SU HIF-4 Carbs. I need to replace it and I was wondering if an HP type SU fuel pump from an earlier MGB will work in place of my current one. According to Dave DuBois' site (http://www.custompistols.com/cars/articles/dd_su_fuel_pumps_101.htm), both pumps can develop the same pressure, but the HP type has a lesser flow rate. Does anyone know if this will be an issue?

Now for the whole story:

As those of you have read my previous posts know, my MG was garaged (not running) for 15 years. When my friends and I sought to resurrect it, we quickly found that the fuel pump wasn't functional. After removing and inspecting the pump we found that it had a broken gasket and that the points were severely corroded (and not transfreeing current). We cut a new gasket from corkboard and sanded the points--and voila, working fuel pump. But we knew that sanding the points would only be a short term fix. The points were still pitted, and they would corrode again fast now that we had sanded off the protective coating. I bought new fuel pump points; but I put off installing them because the car was running well.

Recently, the car started running poorly and sputtered at higher speeds (as if from lack of fuel). So I endeavored to replace the points. I can now report that replacing this small part is surprisingly difficult. In my first attempt, I got the old points out and the new ones in just fine--but the rocker wouldn't move. I consulted the shop manual and, for the life of me, couldn't figure out how to configure the points gap correctly. Further complicating this, the adjustment for the points involved removing all the connections and spinning the whole unit on a spindle. So every adjustment attempt involved removing and replacing three screws with three fragile wire leads, a finicky diode, and the points contact shaft. A friend and I finally figured out that you adjust the rocker gap by bending the little bar arms on either end of the rocker (the manual makes no mention of this, it only mentions the correct gap size).

Unfortunately, in the process of adjusting the points, we broke the connectors off two of the fragile wire leads. Making this problem more difficult, there is almost no excess wire to work with in the pump (which is part of why the leads broke off so easily in the first place). Ordinarily we would have given up here until we could get our hands on a new fuel pump; but there was a large car show, swap meet, and tour the next day that I had been planning on attending for quite some time. So we managed to bodge some new wires to the old wires. Now the car could start and sort of limp along. Of course the points weren't really adjusted well, but we weren't about to fool with it more (lest we break it further). I made it out to the show with the car and managed to purchase a used fuel pump at the swap meet for five dollars. I've tested this pump and it seems to work fine. Its points look good and are properly configured. Unfortunately it's an older model SU fuel pump. It appears to be a polarity ambivalent HP type pump (although I'm not sure how to tell the difference between and HP type pump and an L (low pressure) pump).

I've read Dave DuBois' informative site (http://www.custompistols.com/cars/articles/dd_su_fuel_pumps_101.htm), but I'm unsure whether I'll be able to use this pump in my car. I know they used the HP type pump in the earlier model MGBs with the HS-4 carbs. Does anyone know whether the HP type pump will work well with my HIF-4 carbs?

As always, any help is most appreciated.

Jeremy
1974.5 MGB

J. Palgon

Jeremy - The early MGBs used the HP pumps with no problem, so I would have to assume that they will work on the later cars. They do not have the pressure and flow smoothing chambers that are on the AUF 300 or AZX 1300 series pumps, but for average driving this should not cause a problem. What you need to determine withthe HP pump is that it is working ok, since I assume that it is a used pump. If it has been sitting for a long period of time, it may not want to run when power is applied. If this is the case, remove the end cover and clean the contacts on the points with some 400 grit sandpaper, this should bring it back to life. If you are not in a big hurry, I can restore your AUF 300 pump and convert it to solid state, but it will be about 6 weeks before I can do it. I am going into the hospital this coming Monday to have an enlarged spleen removed, so it will be about that amount of time before I can do any real work.

You might also want to consider installing a permenently installed back up pump while you are working under the car. If this sounds like something you would want to do, e-mail me and I'll send you instructions and what pumps to consider using. Good luck - Dave
David DuBois

David,
Thanks for your reply; and your wonderful webpage. I'm sorry to hear that you're going to hospital. I hope all goes well.

The pump I acquired is used, but working. When we hooked it up to power it made the typical thump, thump sound. I also checked the points and they look good (unlike my old ones). Just to make sure this new pump works, we tested it with some water and all seems to be well.

This issue with my old pump was that the points were just awful. The contacts were totally flattened (not even a nub remained). I could have sanded them again, but it would have been a temporary fix at best. The real problem with that pump right now is that we couldn't get the new points installed with the correct gap--and in the process broke two of the wire leads from the coil. We hastily soldiered new wires to the stumps of the wires now coming from the coil in order to make it to the car show. But I certainly don't want the reliability of my fuel pump to rest on my soldering ability. So in order to restore that fuel pump, I'd need to open it up and replace the wires from the coil to the points. And after that, I'd still have to configure the points correctly again. Is this something I should try to do myself? Do you have any tips for doing this?

Also, as this would probably take me some time, I'd probably want to try this other pump in the car in the meantime--just so I could keep the car running. But this leaves me with another question: Since both the L and HP type pumps loook the same on the outside, how can I tell whether this new pump is an HP or L type pump? Clearly the L type would be insufficient for my MGB.

Thanks and I hope all goes well with the spleen removal.

Jeremy

J. Palgon

Jeremy - There are two ways to determine if the pump you have is a low pressure or a high pressure pump (both pumps are L types), is to either measure the pressure produced by the pumps (difficult to do accuratly) or measure the diameter of the coil core. The low pressure pump has a coil core that is little over 1/2" in diameter, while the high pressure pump is about 3/4" in diameter. The problem with this method is that either the pedestal (that holds the points) on the top of the coil housing has to be removed to see the coil core, something that you have experienced, is fraught with hazards of broken wires. Probably the safest way to determine if the pump will work is to install it and try it out. If it is a low pressure pump, it may work, but it would be marginal at best and probably not handle hard acceleration as they are designed to operate in the engine compartment, where they are mounted at approximately the same height as the carbs. The other alternative is to go to NAPA and ask for a Facet pump, part number 610-1051, or the Carter pump (Federal Mogul), part number P60504 or the AIRTEX model E8016S from Auto Zone. Any of these pumps cost around $40 and will work fine for the MGB. These are the pumps that I recommend using as a permenently installed back up pump.

As for restoring the original pump, thisis not something that I would recommend that someone without some knowledge of how the pumps work attempt, expecially where wires have been broken off and are too short to reach the terminals. Additionally, restoring the pump using the original points, will just result in the same problem that you have already experienced. If the pump sits for extended periods of time unused, the points develope an insulating film ont he contacts and will not work without first sanding them. Further, if the internal swamping resistor internal to the coil housing is burned out, the points will burn rapidly and have a short life span. When I do the pumps, I replace the points with a magnetic reed switch and magnet to trigger a transistor, which in turn drives the pump. This set up doesn't have the problems with burned or filmed points and will continue to work properly, even if left unused for several years. If you will send me your e-mail address, I'll send you information on my SU fuel pump services. Good luck - Dave
David DuBois

Dave,
I suspected that it would be difficult to tell the high pressure pumps from the low pressure ones without an accurate measure of pressure or by installing it and checking. I think I might try and hook it up today just to check. I sent you an email a minute ago regarding pump options.

Jeremy
J. Palgon

Can't help with the pump question, but Dave, I wish you a speedy recovery!
Rob Edwards

Dave, I want to wish you a speedy and complete recovery.

Clifton
Clifton Gordon

Thank you all who have wished me a speedy recovery. The doctor said that I will be out of the hospital and able to drive in no more than 5 days (I don't think that he is aware that all we own is stick shift MGs). Removal of the spleen is apparently right up there in degree of difficulty with appendectomys. He said he is schedualing 1 hour for the surgery, but expects that it will be complete in more like 30 minutes. I hope that he is right, I don't look forward to the hospital stay - can you say booring? Cheers - Dave
David DuBois

This thread was discussed between 18/09/2005 and 19/09/2005

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