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MG MGA - S.U. Fuel Pump


Looking for some help with intermittant operation of S.U fuel pump (points type). Working on the principal that 90% of fuel problems are ignition related, I replaced points / condenser, checked the primary circut, checked for spark etc and all ok. This was after I had removed the pump to clean points, check / clean the filter.

Until I removed the pump to clean the points it was working ok, except at start up when the pump on occasions it "buzzed" after the familar click, click. Since removal and refitting when starting from cold, with an ambient temperature around 12 degrees centegrade the car starts ok and will drive for about 500 metres then the engine stops. Last weekend when this happened after turning the ignition off and on a few times the engine could be started and we were able to travel on a 250 mile round trip, including a stop for lunch etc and no further problem. However when starting from cold the same problem was experienced later in the week.

I am prreparing the vehicle for a 3,000 mile trip commencing in three weeks and keen to get the problem sorted.

Any help would be appreciated

R J Goebel

I assume that when the car won't start the engine/starter turns over; It sounds as if you have a defective fuel pump; I installed an inline solid state electric fuel pump that can be swithed on if the SU fails; Moss sells them for $79.95 (377-420) but I purchased them locally at an auto supply store for less;Barry
Barrett Burka


There's an SU fuel pump specialist on this site (David DuBois, Bremerton, WA, USA ddubois@ who will undoubtedly answer your question, although you might email him if he fails magically to appear. In the interim, it might be helpful to peek through the archives on fuel pumps for a related query. I wish that I could advise you, but apart from tapping it with a screwdriver handle this fuel pump still remains beyond me. Good luck!

Ken Korey

Russell - I would guess that the points in your pump need to be cleaned real well. Remove the upper contacts and scrub the contacts on a fine sharpening stone or some 400 grit sand paper. To clean the lower contacts, remove the mounting screws from the pedestal and carefully fold the pedestal back, pivoting it on the pivot pin through the toggle far enough to expose the contacts, then scrub them as above. If this doesn't get the pump running, You might contact Tony Oliver at He is getting started in repairing the pumps and may be able to give you some help. Cheers - Dave
David DuBois

Thanks Barrett, Ken & David,

I had a look at the points and interestingly the top set were badly discoloured / dirty, the bottom set ok looking except one of the points was considerably samller than the other. The problem with the top set was most likely an operator error (when I cleaned them last week I probably did not reset them correctly (too much haste). So I have decided to fit a new set. Have disassembled the pump and will install the new ones tonight.

My question is now about the diaphragm. In earlier pumps these had to be stretched, as outlined in the workshop manual. I understand this is not so with newer pumps, the pump on the vehicle was purchased in 2001, so hopefully is the newer type. Is there any method to determine if the diaphragm is the newer type?

Also what is the expected life of a set of points, this set has been in the car for about 20,000 miles.

R J Goebel

It could be that you have a restriction in the fuel line which is stopping the fuel pump.
I think there was a similar case on here a while back where someone had pinched the fuel line under the car and the restriction was not allowing fuel to flow quickly enough to the float chambers.
The SU pump may be working 100% correctly but this restriction will starve the engine in a short time.
An aftermarket fuel filter can have the same effect.

Hope that helps.

Neil Purves

Russell - There is no need to stretch the diaphragm. In fact stretching them will interfere with their proper operation. Cheers - Dave
David DuBois

This thread was discussed between 29/06/2008 and 01/07/2008

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