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MG Midget and Sprite Technical - Fuel Pump Diaphragm

Hi,

I decided to service my SU fuel pump. I have no idea if it ever worked before and have been considering buying a new one, so thought I'd dismantle mine to learn how it works and see if there was anything wrong with it.

It all looks very clean and the values operate well. So I am now thinking of buy new points and gasket and that leaves me with the diaphragm.

In the first photo the rubber is in very good condition with no cracks, but the clear plastic film seems to have come away from the rubber. Not sure if this is how it should be or if there is a problem.

Looking at Moss one for reference, there's doesn't seem to have a plastic film, but that might be because it is stuck to the rubber and so more transparent.

Just wondering if anyone has worked on these before and what your recommendations would be...

Put it back together as is?

Replace with new diaphragm?

and yes just buy a new fuel pump is another option!

Many thanks

James





James Paul

This is how it looked when I first removed the top cover.

James Paul

I wonder - has it been repaired before?
I once did a roadside repair of a split diaphragm using a plastic supermarket carrier bag. I didn't remove the damaged rubber, but backed it up with the extra layer of plastic. It was still going strong 2000 miles later.
GuyW

The clear plastic looks very much like mine did.

I rebuilt my pump over 25 years ago, with new points, valves, etc.

After a few years of use, the car came off the road. When I came to refit it to the car after it had been off the road for a number of years, I cleaned up the points, as they had oxidised. I then found that it wouldn't actually work, because the diaphragm had gone hard.
Dave O'Neill 2

James

You might just want to buy a rebuild kit, see: http://sucarb.co.uk/su-fuel-pumps-spares/single-hp-pumps-kits.html

I guess it is a HP, high pressure one, not the low pressure LP one (if the latter, see: http://sucarb.co.uk/su-fuel-pumps-spares/single-lp-pumps-kits.html)

Eminently rebuildable these fuel pumps and the diaphragm does not last forever. Be careful with some of the plastic parts, e.g. the fuel connectors, that can be brittle. Note the gauze filters. Also be careful on assembly as mine had stopped working as the points mounting Bakelite support had a crack from a PO’s over enthusiastic tightening of its mounting screws.

Cheers
Mike
M Wood

£40+ for a repair kit!

Pass the pump on to someone that'll get joy from repairing it - and for yourself get a fit 'n' forget Hardi - https://www.ebay.co.uk/itm/174224085413

To add value to whoever wants to repair the SU don't just give it away to them charge them for it to show you understand how they value it, watch their face light up with a wide smile, and ask for photos of it when it's finished.

I'm always thinking of others. 😊
Nigel Atkins

Rebuild your SU pump, they are every reliable. All you need is the knowledge.

SAD NEWS.
I was looking for SU pump stuff, and found that David DuBois died of cancer in 2019. He posted masses on SU pumps. He was the go to man for help on them. He sent me loads of stuff. RIP.


Anyway, here is a link to his very useful knowledge.

www.dbraun99.com/Dave%20DuBois/

http://www.dbraun99.com/Dave%20DuBois/

You may have to cut and paste the link.

Or search the technical archives here. David DuBois posted loads of stuff on su pumps.
anamnesis

By all means repair it but repair it well so that you can then forget about it but at £40+ you want all the parts not replaced to be almost as good as new too.

Dave didn't seem to have much faith in SU fuel pumps as he not only suggested that a fuel pump was a necessary spare to carry (along with others spares) but to the spare pump plumbed and wired in ready to be switched over to.

Instead of fitting components and parts that need you to carry spares for them or of them fit something reliable and forget about it.

Where does it end, some seem to have the whole car stuffed with spares "just in case", they must love being roadside repair warriors, showing how clever they are to be able to do such repairs, which they are but not as clever as not needing to stop to do any repairs.

Some enjoy the spice of unreliability and think it's part of 'joy' of classic car ownership whereas I've had enough of it to last me two or three lifetimes. Keeping up with the piss-poor quality of modern parts and having to change or repair them is more than enough 'joy'. IIRC the SU electronic pumps/kits(?) were unreliable at one point at least.
Nigel Atkins

Not quite true . Dave DuBois thought su pumps reliable, but like any pump they can fail, and he thought a backup pump was therefore a good idea.

I've got a backup pump, --- on my shelf. I was going to fit it in parallel, but I never got around to it. And on reflection, because I've never had a reliabiity problem with su fuel pumps, I doubt I'll ever get around to it. But I do like the idea, just in case. But again, I also carry a spare wheel. I must be a worrier. Lol
anamnesis

Yes but Dave had the spare actually fitted to the car ready to switch over to, so two pumps fitted, just in case, shows a lack of faith or overwhelming preparedness for an event that should occur once in decades.

I'm not knocking the guy, his priorities were his own but that part seemed overly excessive to me, based on statistics and my experience.

All stuff eventually fails, as I've put before you'd need to tow another complete car behind the one you drive just to be sure! Many of the stops I've had haven't been with the statistically most likely so even if I carried all the parts some do it wouldn't have helped, prevention is better than cure. Though I accept prevention can fail, especially if you pay a slack professional to do the work and there's plenty of them about.

I feel all this stuff about carrying spares perpetuates the belief and practice of classic cars being more unreliable than they are (or should be) and also leads to this nursing them along instead of driving them as intended.

I'd sooner be at the pub stop than being a roadside-repair-warrior, in the rain with water running down my back on to my underpants (as has happened to me).

On one weekend tour the Elan Sprint come flying by me, great to see it driven as designed, but a mile later it's in a pull-in with bonnet up and CB points fiddling, I saved him a seat at the pub. 😊
Nigel Atkins

The most unreliable thing on my car, which has left me stranded now 4 times in the last 100,000 miles, is the fuel.

No, Nigel, not the original SU fuel pump, but the fuel in the tank. Or rather, when it isn't. In the tank. It does keep running out. But for that I do carry a spare (can).
GuyW

Yes but as my wife often points out to me the can does need to have fuel in it - which of course mine always has (unless I've forgot I've emptied again, often for others cars that are low on fuel).

One of the reason I bought my car was for the 7 gallon tank, first full fill up confirmed it wasn't even 6 gals unless filled to near the petrol cap.

It was a couple of decades back that my wife refused to push any car again that had run out of petrol, and it's not like I wasn't busy steering! I've had to put up with a lot!
Nigel Atkins

This thread was discussed between 06/04/2021 and 07/04/2021

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