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MG MGB Technical - Fuel Pump

Gents.

I'm having to change the fuel pump on my 1980 1800CC mgb roadster. I've developed a fuel leak (quite bad) and I'm not sure if it's the pump it's self or the fuel line where they connect to the pump (they are quite brittle at the connected ends). The leak is from 'above' the pump so impossible to see exactly where it's coming from.

I've got the old pump out and have a new pointless electronic pump (from MGBhive) which I'm about to fit.

My problem is that the old (original) pump has a vent line connected to it but the new one does not have any provision to connect a vent line. Is the vent line to vent the pump it's self or does it vent back from the engine/carburettor (the line comes from 'the engine end', but I haven't had time to trace back yet).

As the new pump has no vent connection point what do I do with the existing vent tube, does it need connecting or can it be left to vent to 'fresh air'.

(When the pump is sorted I can then get on with replacing my leaking core plug - see other thread).

Thanks.
Brian Davis

Just to clarify this is the vent line pipe (small dia). The main fuel line is the one above my finger.


Brian Davis

Brian,
the vent was for the old (SU) pump internals (air displaced by movement) don't need it on the modern electronic.

If it's a Hardi (or copy?) you got as per photo then I can flood you with info if you want.

Did the pump come with fitting instructions or any paperwork or model number on pump?

Welcome to the world of fit and forget rather than fit and fart about.

(the BBS is awash with fuel pumps at the moment)



Nigel Atkins

Hardi pumps and others like Moprod don't have vent ports. I don't see why being electronic is the deciding factor as the only difference is a transistor to power the solenoid and not a pair of contacts, the solenoid moves a reciprocating diaphragm just the same - that's the clicking you hear.

I can see why at least one is needed as when the diaphragm is pulled back by the solenoid without a vent it will compress the air behind it, which would make the job of the solenoid harder. It's quite possible the Hardi does have a vent somewhere, without the port to connect a tube.

Electronic SUs are shown with and without ports according to application, at least one having a small hole in the body but no port for a tube. Just tie the tube up out of the way for future use if needed. If you pull it out it leaves a hole into the boot, or the chassis leg on late models.

Why the SU increased from one to two is a bit of a mystery. The ones with two even have a one-way valve in the one on the cap so air is effectively pumped through as the diaphragm reciprocates.
paulh4

Nigel. Picture of the new fuel pump. If I read your post correctly your saying that the new pump does not need a vent.

Only simple fitting instructions supplied with the new pump with no mention of what to do with old vent pipes.

With the old pump and assuming it a vent pipe why was the vent pipe taking so far forward to discharge, I would have thought it just needed a local discharge and not piped away.

I'm assuming that the vent pipe can therefore be left hanging (out of harms way) under the car.

Thanks. Brian



Brian Davis

Brian,
sorry I'm not the best writer, no you do not need any vent pipes for your new pump.

I'm not technical so may use wrong words/terms - the pipes not for venting fuel vapour but for fresh air to allow free internal movement (of the diaphragm(?) I'd guess).

Never leave anything just hanging, gets confusing in the future either remove it and put in blanking grommets or strap them up if you want to keep them (but why?).

Keep things tidy to make things easier in the future.

Talking of which - I'd not be happy with that ring connection, a little wire showing that the wire is fully through the fitting is ok but not before the fitting, full insulation up to fitting with wire sleeving and fitting insulation.

Try to get the crimp on the fitting so that the split in the metal part of the fitting is parallel with the jaws of the crimper tool so that split compresses in the right way to crush the fitting to the wire.



Nigel Atkins

Paul,
the Hardi pump has a 0.2mm hole in it, don't ask me where as I can hardly see 2mm let alone 0.2mm - but I have a 0.2mm gauge wire I can photograph.
Nigel Atkins

Nigel - No problem. For a non technical person you know a lot. Great help.

I agree about the wiring connectors, they need looking at. The live is through into the boot to connect to the wiring loom anyway so that will need looking at.

Now I know the vent pipe is of no use yes it needs tying up out of harms way or removing (depends on how easy it can be got at).

More important at the moment is the main fuel pipes, they are brittle and breaking at the bango connections onto the pump. The pipe ends need cutting back to 'good' material (OK for the fuel tank to pump line but I'm not sure if there is sufficient slack in the link to the main engine fuel line - another reason to crawl under the car tomorrow).

Thanks all for your advise.

(Then back to the original job - the core plug replacement)

Brian
Brian Davis

Brian,
not really just that there's been a lot on petrol pumps last couple of days - and I'm often wrong.

Those breather pipes will be plastic so just cut them either side of any fixing and remove, remove the fixings if you can but if not no worries. T-pieces could stay or be replaced with blanking grommets later.

I'd always renew aged fuel hose with good quality modern 6 and 8mm fuel hose, if you can do the connection to banjo connectors now, they might not last as many decades as the original but if the existing are breaking up it's a risk as to how long they will continue to last might be years but it might not, piece of string thing.

Isn't old rubber great for transfering and spreading dirty grime. :)
Nigel Atkins

Tell me about it.

It's surprising (or maybe not) now much dirt and muck comes off the underside of the car when your lying on your back underneath it.

Brian
Brian Davis

Could be worse could be rust. :)




Wear eye protection.

Nigel Atkins

About twenty ago I fitted a Moprod pump to replace the old SU. It looks similar to the pump shown in Brian's picture, and has worked well.

No vent tube required.

Random thoughts:

One issue I had was that it was very easy to strip the thread in the plastic body when reconnecting the banjos. Luckily, I managed to repair mine with PP Supersteel (like JB Weld), and this has held for years.

An issue I had with another car is that if you've still got the steel brake pipes, if they're fairly corroded, when you move them they can split and leak.

I recently replaced the fuel tank on the B and it took ages, and more torque than the ideal, to get a fuel tight seal at the tank outlet. So it might be a union on the pump, but as said above don't overtighten!
Peter Allen

If the hoses at the pump are ratty don't cut them back looking for a good piece! Just replace them, and don't use braided as you will need to inspect them carefully annually.

I changed the V8 hoses a while ago because the braiding was really crusty, and had been the 20 years I'd had the car. Slit the rubber and opened it out and they were perfect (1st pic). But I've had to replace hoses in the engine compartment more than once (OK it's hotter, but they should be able to cope with that).

Roger Parker wrote in the MGOC mag recently about the effects of Ethanol:
"I have seen issues in a couple of my cars where some newer hoses (reputedly ethanol resistant) have split whilst older original equipment on my V8 EFI roadster still carry on with no problem."
Which confirms what I've been saying for ages - it's not the ethanol, it's crap rubber.

I ordered a metre length of Cohline from Moss but they sent Codan. However I see now they supply Gates Barricade multi-layer and Peter Ugle had multiple problems with that of bits of rubber appearing in the fuel filter and the float chambers and causing fuel starvation (2nd pic). The inner layer was very thin and shredded when pushed onto ribbed ports. If you can, get the correct 1/4" and 5/16" hoses, don't force under-sized hose on. It's the clamp that makes the seal.






paulh4

This thread was discussed between 10/06/2020 and 11/06/2020

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