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MG Midget and Sprite Technical - 1275 Fuel Pump, Fuel Starvation (Q Anthony Cutler)

Hey everyone,

Long time no see. It's been about 6 years since I used to frequent this BBS and about the same time since my '69 Sprite last saw the light of day, having been hibernating in the garage since 2005 after installing an Engine/Gearbox combo I bought off Anthony.

It still looks like the day I closed the garage door though, with the exception of a hole in the drivers seat where a mouse has added some leather features to its nest, and I'm determined to get it back on the road.

Anthony - I sent you an email this morning but I've no idea if you still use your hotmail account, so I'll post the Q here too.

I attempted to get the Sprite started the other week and took the plugs out to crank the engine over to get the oil pressure up before attempting to fire it up. After replacing the dead battery and sorting out the sticky starter motor which wasn't throwing out, the fuel pump was the next problem. I've taken it apart and it was obvious that the point were just corroded which is easy to sort, but it got me wondering about a problem I was having with the engine when it was running regularly. It used to go about 12miles before starting to run like it was being starved of fuel. I'd have to stop at the side of the road and leave it for 10mins before it would start and run again. I'm wondering whether this was anything to do with the standard fuel pump I was running? Did you just run the standard AUF214 pump? I'm thinking perhaps it doesn't pump enough volume of fuel for the SU 1.75" carb and that was the reason it was conking out.

The engine's had a fair few modifications so perhaps I the fueling demands have increased beyond what the standard pump is capable of supplying?

Thanks for any help anyone can give!



P.S Attached a photo of the Sprite, some people may remember her from a while back!


If it ran for about 12 miles and then you had to wait for it to fire up again, I would look first at the fuel cap causing vacuum in the tank. If that's OK it could be a long job to find the fault. Start with fuelling then go to the ignition. Good luck

Mike J Pearson

Maybe the points where already bad, causing the pump to run hot. Had that with my MG1300.

See also "Fuel delivery prob.."
Alex G Matla


The capacity of a standard pump is in excess of what
is needed for a single HS6/HIF44.

Could be pump not up to it as per Alex, try running it into a container - output is quoted in manuals (can't remember currently) see if it slows down etc.

Also check coil is not dodgy as can cause problems simmilar and not easy to trace - if you have a spare try a swop.

richard boobier

Thanks for the info guys, all very helpful.

Alex, it seems like exactly the same issue I was having, especially under load.

Richard, that's a good idea. Alex's link suggests (via David DuBois) that it should be able to fill a pint container in under 30secs. Given that I'd need to overhaul the old SU pump with a new gasket and diaphragm to replace my torn one (yes, twisting wouldn't get the two halves apart so the screwdriver came out with obvious consequences) I'd likely be paying about 25 anyway, seems that 50 would get me a solid state SU pump which would be more suitable to the cars longer winter hibernations, preventing tarnished contacts from happening again.

I'll get a new electronic pump ordered this week and stick it under the car and see if I can get her going again.

If I still have the problem I'll look at the fuel cap vacuum theory and maybe also dirty fuel filter too. The aftermarket inline filter in the engine bay is clean, as was the one in the fuel pump and I can't remember there being a filter in the tank itself?

Others have reported problems with crud in tanks causing a partial blockage at the outlet and intermitant reduced flows !
Another one not easy to identify.

richard boobier

Hey robin,

I remember you....

Just another thought...being that we are all throwing steaks up agiant the wall to see what sticks....

The hose/tube from the float chamber to the carb might be partially clogged, when it starts to do this pull the choke cable and see if it improves

ny vacume leaks, valves arent adjusted to tight

So what happened to you... Join the foreingh legion, become a full time roaddy for the lawerance welk polish dancing troup, coma, ....perhaps a boy????

Welcome back


Robin - The 1 pint (US) in under 30 seconds is for the AZX 1300 pump that put out over twice the volume of the AUF 214. The AUF 214 pump should pump 1 pint (US) in just under 1 minute (8.4gph or 1.1 ppm). If the pump is getting hot to the touch, then you either have a clogged tank vent (Probably through the filler cap) or a partially blocked inlet line to the pump (most likely a clog in the pickup tube in the tank. A clogged tank vent will shut off fuel flow quicker when the tank is full than it will when the tank is only partially full (a partially full tank has a greater head of air above the fuel and take longer to develop sufficient vacuum to stop the flow of fuel). You can check if this is the probllem just by loosening the filler cap.

There is another potential problem that will often produce the same symptoms as fuel starvation and that is a flaky ignition coil that is in the process of dying. You might want to check this out if the fuel aspect leads you to a dead end. Cheers - Dave
David DuBois

Hey Prop, oddly enough I remember you too and you're still your same crazy self!

Ach, you know how it is, the British government approach you and ask whether you're interested in perhaps doing a bit of work for them, one thing leads to another and before you know it you're playing high stakes poker with high class criminals, jumping between the roofs of buildings in pursuit of various henchmen and driving around in supercars with gorgeous girls hanging off your arm.

Well, maybe only one of those is true but I think in reality moving out of my parents house in the country (where the Sprite lives) and into my own flat in the city led to me not having the money to keep her running and the taking up of various outdoor pursuits led to me not having the time. My good old pops had been nagging on about getting the Sprite back on the road for a while so the other day (as a father-son bonding thing) we donned our boiler suits and rolled her out into the sunshine. Now I'm determined to hear that little A-series burst into life again!

Yeah ... Life has a way of upsetting the apple cart

Welcome back, and good luck with the sprite

Sucks about the leather seat and the mouse


I've just bought a new electronic fuel pump ( as a diaphragm/gasket kit for the old one was only a tad less.

I've noticed it doesn't have any breathers anywhere on it. The bit of paper that came with it claims that you "shouldn't seal around the end cap where it slides onto the pump body, as the pump breaths through this". This doesn't really explain why it's got blue electrical tape round here then!

I can't understand how the diaphragm doesn't cause a vacuum inside the pump?

Is there really no breather required here, or is there something awry?



I've got that one on my UK spec '73 1275 put it on without breathers

it's been on there 4 years working fine

I just maked up electrical connections with black and red tape on the pump body for future reference
N Atkins

Robin I think that type may breathe through the tiny gaps where the electrical connection pillars pass through the plastic end cap.
David Smith

Robin - Check around the base of the coil housing. If there isn't a spigot somewhere around the base, there will be a small vent hole there. The back side of the diaphragm does, in fact, pump air back and forth and has to be vented outside the pump or the pump would become unstable. See the article, SU Fuel Pump Vents in the SU Fuel Pump Articles section of my web site at: Cheers - Dave
David DuBois

Thanks for the help everyone, think it must breath through the electrical spade connectors as David said - it's the only place on the unit that has the slightest of gaps around it!

Thanks for the link David, I spent a good while reading through your site a week or so back ;)

Robin - There should be no venting through the end cover around the power terminal spade connector, there is a seal on the inside of that opening. The attached picture shows where the normal vent spigot is located. I have seen cases where the coil housing used for the AUF 214 has not been drilled. In the next post the attached picture shows where you can drill a hole in the coil housing to provide proper venting. Cheers - Dave

David DuBois

The attached picture shows where a 1/16" hole can be drilled in the coil housing to provide proper venting for your pump. I would only do this if the pump becomes unstable or displays other problems due to no venting. You may not experience any problems due to the lack of a vent on the all electronic pump as the diaphragm doesn't move as far as it does on a points style pump.

If you do have to drill the housing, first remove the diaphragm (e-mail me at for information on how to put the diaphragm back into proper adjustment) before drilling and then drill perpendicular to the slope between the side of the housing and the flange where the red arrow is pointing. Cheers - Dave

David DuBois

My old AUF214 had a vent in the location your picture shows it. I'm guessing if the Electronic one doesn't have one then it must funtion without it. As you point out, if the diaphragm doesn't move as far then venting may not be as much of an issue.

Oddly enough my mate Craig's been having problems with his fuel pump in his 2003 Ford Mondeo. He hauled the pump out (which is located INSIDE the fuel tank!) and found that the wires had bared and were causing intermittent contacts.

Initially I was confused as to how he hadn't been blasted into space, but apparantly it's got something to do with a lack of oxygen in the tank which prevents combustion. I would have thought there would be a fair bit of oxygen in the tank when it was running near empty?

Robin - Even nearly empty, the fuel fumes exclude sufficient oxygen to support combustion. For combustion there needs to be around 17 parts of oxygen to 1 part fuel. Also, I dare say that the fuel pump for his car is considerably more expensive than the AUF 214 for you Midget. Cheers - Dave
David DuBois

That's very interesting, you really are a font of knowledge on all things petrol-y! Yes, his pump cost 200 :)

This thread was discussed between 01/10/2011 and 16/10/2011

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