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MG MGB Technical - Fuel pump, electric or not?

I own a 72 MGB and recently the fuel pump died. I'm wondering whether the new one I purchase should be electric or not. Any major advantages? Thanks for any help.
CG

This is one of the oldest debates on this board. The "modern reliability" of electronics (pumps, distributors, etc.) vs. the servicability and "limp home-ability" of traditional points in pumps and distributors.

The problem with many of the electronic stuff we get for the aftermarket is that it's not just up to snuff with the stuff you get on a modern car. Sometimes the pump mechanism is fine, but the housing is not as robust as a trad SU. If your fuel pump fails, and its electronic, you're SOL, while an SU will slowly fail - you can usually whack it with a hammer or heavy screwdriver to jar the points enough to get home, and then you can repair/replace it.

You pays your money & takes your choice. One strategy would be to get a new pump (points-style or electronic - your choice) and install it. Also buy a set of points and spend an hour to replace them on your old pump - and you'll always have a spare to carry.

Lots of fun argument in the archives, though.
John Z

I think a really, really good way to go would be to simply wire up two working fuel pumps, and have a switch up front that selects one or the other. That way, if one craps out while you're on the way to a black tie affair with a decked-out brunette on a rainy eve, you need not suffer the indignity of attempting to invigorate a dead pump by stepping outside, leaning under the car and beating the pump ... you just flick the switch and voila. For the backup, I'd just use a modern-style Purolater cube pump ... kinda noisy, but you won't have it turned on a whole lot.
Ted

CG-
When an SU fuel pump fails, it's usually because of the points going bad. This problem normally takes many years to develop. I have the solid state version of the SU fuel pump in my car. It even clicks like the original points-type pump. To protect it I installed a fuel filter in the line that connects it to the fuel tank. Works fine.
Steve S.

Does anybody know how the original pump will stand up to running dry for a not TOO long period of time? Not really a big concern of mine, but would be interesting to know...

Anthony
Anthony Morgan

CG - send me a private e-mail for a write up of my SU Fuel pump services. I can restore your pump and convert it to solid state (electronic) for a lot less than the price of a new pump.
Anthony - the SU pump is not harmed by running it dry as it does not depend on the fuel flowing through it to keep it cooled. Greater harm will be done to the pump by having a clog on the input side of the pump. This causes the pump to fail in a current on condition which will cause it to get hot, usually burning out the swanping resistor in the coil. This in turn causes excessive arching at the points and reduces the life of the pump. This is why I do not recommend placing a filter between the tank and the pump. It is also the reason I recommend keeping a eye out for rust forming in the tank, which will migrate to the pump. I saw one pump literally packed full of rust particles. This was on a pump that I had restored for a customer and had told him that i saw enough rust in the pump initially, that he should check out the tank. He finally did something about the tank after paying me a second time for fixing his pump.

Cheers - Dave
David DuBois

I faced the problem with the original 35 years old SU fuel pump fitted on my MGC last year.
Yes, the points were worn out, and yes, I did not face a sudden interruption of fuel supply but repeated, limited and gradually increasing engine misfiring (air/fuel mixture too weak).
---
CG, unless you want absolutely to keep your BGT in factory condistion, I would recommend to adopt "solid state electrics" technology.
---
You did not mention if you are in America or in Europe.

In Europe, the MG Owners Club UK proposes 2 "solid state electrics" fuel pumps which retain original SU diaphragm mechanism, while the points are replaced with a printed circuit.
One model has a plastic body and clicks like a colony of grasshoppers. The 2nd one has a metallic body and is the one I recommend. MGOC did not offered any conversion of original SU pump to "solid state electric" and the 2 suppliers I contacted were charging more then a new MGOC unit.

If you're in the US, David's offer might be worth to consider.
---
I also join David's comment on fuel filters installed at the inlet of fuel pump : with both the old SU and the new MGOC unit, fuel supply is interrupted with level below 1/3 of tank.
I've installed the fuel filter just before the carbus, but - David is right once again - this is not a protection against rusted tanks.
Guillaume STUTTER


I've been thinking about this recently as I've looked into preparing my B for historic road rallies. I've recently had a modern electronic pump put on, but I'm not sure if this is the best as other people have mentioned.

What I have seen some people do with B's is mount the fuel pump in the boot and then use a double header SU pump off a Jag. I'm not sure if this is the same princple of having 2 pumps - if one end fails the other will keep going. Anyone know?

If you were to install 2 pumps, how would you rig up the mechanism to switch between them?

Cheers,
Jamie
jamieo

The best bet would be to fit a belt-driven pump.
It is fitted in the engine compartment like the alternator and driven by the fan belt.
This way you eliminate all possible electrical hassles and have another bonus: when the fanbelt breaks you cannot overheat the engine because it dies from fuel starvation :-)
Joern

This raises a good point ... the mechanical fuel pump isn't driven by the fanbelt though, rather it's driven by the cam. There's a boss on the 1800 engine for a mechanical pump, but I've never seen one used. If you could find the correct one (again, it's gotta exist or that boss wouldn't be there), that should be the end of fuel pump troubles once and for all. These things are good because any time the engine stops, obviously it stops pumping fuel. Hugely safer in an accident.
Ted

My experience has been no complete failures with electric pumps, but I have had mechanical pump's diaphrams fail and cause the oil to be diluted by fuel. This is considerably less safe than having your fuel pump continue to run after an accident, and your fuel pump can be powered from an oil pressure switch if that is your worry.
George B.

Ted, you'll need to find a cam with gears to drive a fuel pump. That's going to be quite a project right there.
Wade Keene

I too have questions on this. If you have a backup pump installed will it draw fuel though the SU pump? If you had a double pump wouldn't the points wear out at about the same time?
Wiring the pump to the oil pressure switch would require an ignition switch circuit so you could start the car. I suppose the inertia switches work well, you never hear a lot about car fires from wrecks.
Philip A. Smith

jamieo - You can set up the double ended pump such that only one end was pumping at a time, I do this when I am testing that type of pump. If set up that way, the points on the end not running would not wear out at the same time as the working end. I would, however recommend that each end be run on a regular basis to keep the points from developing a film on them which will insulate the points and thus keep the pump from running.
Philip - Yes, one pump will pump fuel through another one regardless of the brand. They all use check valves to keep the fuel from being pushed back into the tank, but will allow the fuel to be pushed (or pulled, depending where the pump is located) through to the carbs.
Cheers - Dave
David DuBois

Wade, it's usually just an extra lobe on the cam rather than gears. The lever on the pump just rides along and gets pushed up and down, and voila. There _must_ be a cam for this given that the 1800 block has a boss for the mech pump!
Ted

Hi Ted,
Duh, I remember now. a lobe, not a gear. So you'd have to find a B series with the lobe to drive a fuel pump. Not easy, I'd bet. Marinas and what else(?) used B series, but did they use mechanical pumps? And once you find a mechanical pump cam, it would surely need to be reground. Is there room for a fuel pump right there by the exhaust manifold?

By the way Ted, I had heard some time ago that there was an MG museum in Keene, New Hampshire. Do you know anything about this, one way or the other?
Thanks, Wade
Wade

The part of the cam which operates the mechanical fuel pump is known as an eccentric lobe or eccentric cam. The factory MGB can has this on the front part of the cam. There are four egg shaped, eccentric lobes and a circular shaped eccentric lobe. The circular lobe could be used to power a mechanical fuel pump. To do so would use a small amount of the engine's power. I have seen more problems with mechanical fuel pumps, both failing to pump and the diaphram leaking gas/petrol into the crankcase, than I have seen failures with electric fuel pumps. Do not know, exactly, how long a good SU pump lasts. More than five and one-half years. This was on a new B driven for that length of time as a daily driver. The SU pump on my GT was replaced with a new, points type, SU four years ago. Have no idea of the age of the pumps on the other cars, except "they look old". So did the one on the GT which finally went out. A single pump will last for years (five or more to my personal knowledge). Thus, if some one has concerns, purchase a new pump, install it, ship the old pump to David DuBois for rebuilding, install the rebuilt pump in five years and ship the other pump to Dave for rebuilding. That way, you can almost guarantee you will never have a problem. Les
Les Bengtson

I just looked at an old cam that came from my 68 GT, the correct fuel pump lobe is already on it. Fuel pump lobes are just an off centered circle, as used on millions of older US cars. The exhaust manifold would not present a problem but the steering pinion shaft is about 4 or 5 inches away. The Metropolitan used a BMC engine and a mechanical fuel pump. See a photo at;
http://arcticboy.com/Pages/arcticboysmet.html
A photo of an engine with mechanical fuel pump is about 20 photos down. I believe it used an Austin A-40 engine. I hope this link works.
Clifton Gordon

Guys
Bromsgrove MG Centre were selling a Quinton Hazell electronic solid state pump (QFP172E) as a direct replacement for a AZX1307 for 44.00 UKP at the Stoneleigh show last weekend. I have bought one for my "C" and it is dimensionally identical to the SU and looks very well made with an all metal body. Proof will be in the sucking!!
Peter
PETER JEVONS

GC,
I am no fan of SU fuel pumps.
After mine took to stopping on the top of the "West Gate Bridge" here in Melbourne (5 times & no where else, just there, I think it liked the view)I used a second hand fuel pump off an 82 Subaru. Just stuck it in an unused corner of the engine compartment and bypassed the SU . Worked perfectly.
Peter

The question was 'electric or not?' and of course all MGB pumps were electric. As to pointless or not, my V8 came with one and I had to junk it as it started pumping erratically from time to time and I just had to wait until it decided to start working properly again whereas one can usually get the pointy types working with a thump. I'd never use a 'pointless' one again.
Paul Hunt

This thread was discussed between 18/02/2003 and 21/02/2003

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