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MG Midget and Sprite Technical - Electric fuel pump problem

I have an SU fuel pump mounted on the rear bulkhead. Yesterday I replaced the hoses as they had perished (one was soggy and fell off). Today I turned on the juice and the pump ticked away as usual, and then kept ticking. It would not fill up the carb and stop as it should. I disconnected the hose to the carb and fuel pumped, but intermittently. I took the pump off and checked the diaphragm and the valves. All perfect. Valves working fine. Tested the pump off the car - fuel flowing perfectly. Back on the car the problem was just the same. I wondered if wasn't priming as tank level was low, so I put another gallon in. No difference.

The pump has a Burlen electronic kit which has been fine for 10 years. They also fitted a new coil at the time. I am stumped, and need the car this evening!

Les
L B Rose

Quick thoughts

. partial blockage on flex-hoses, hard lines or from tank

. poor seal of joints sucking air in

. put compressed air through open ended pipes going from both ends (to check for one-way valving effect of any secreted crud)

. check electric supply, live and earth

. when all fitted in situ check for any interference from the installation or surrounding items

. was your bench test as if fitted to car, fuel storage container, pipe, pump, pipe, catch container

. get someone else to drive tonight and enjoy responsible drinking.
Nigel Atkins

Thanks Nigel. I forgot to say that when I disconnected the hose from the carb, the fuel pumped OK and the pump stopped when I blocked the hose. Can't do the same test with the pump off the car as I don't have enough hands! I will have to work out how to do that. I suspect the air sucking is most likely as those plastic connections are not well clamped by design. Maybe the seals have hardened. But there are no fuel leaks anywhere.

Wife will drop me off at choir rehearsal tonight and I can get a lift back.

Les
L B Rose

Les,
I'm amazed at you, you don't have full sized mock up test rigs or another spare whole Frogeye to do test work on and rely on actual road use!

I forced a 6mm rubber fuel hose on to the 8mm/5/16" connector of my Hardi electronic pump recently, and put a jubilee clip on, I've got a feeling I might need to cut it off when I replace with 8mm hose.

Of interest to you perhaps was that the 5.5" length of 8mm (very hardened and cracked) hose has a couple of small lines where the hose is slightly flattened as if a couple of fine slices had been taken out but worn down rather than cut. I've no idea why but will investigate later.

Like you I wanted to use the midget but smelt petrol at start up and then had a really enjoyable time squeezing under the back of the car to lay just reaching the hose clips, having to close one eye to see one clamp because I couldn't get closer. Forcing the 6mm on to 8mm done my op recovery very little good. Luckily it was a pleasantly warm day and we were still able to go out for a ride. Oh the sheer joy of a near roadside repair.

Of course, had circumstances been different but they weren't, I had intended to replace the fuel pump flex-hoses a while back (but not the 12 year old Hardi electronic pump) when I dropped the tank to replace the sender seal (again). Obviously now I have the added frizion of the other flexi-hose giving out before I'm able (or can be ar*ed) to do the work. If this happens I will use my tried and test repair method of driving fast to get home before the fuel runs out, I do the same when the fuel is running out in the tanks, only failed a few times.
Nigel Atkins

Ha ha! I was very proud of myself the other night when the hose fell off just round the corner from home. I just needed to jack the car up, remove O/S rear wheel, giving access to the pump so I could get the hose back on. I am now far less proud. I will trot off to Burlen Services tomorrow (they are only 2 miles away) and get some new valves, and anything else they think it needs.

Les
L B Rose

Les, there is a situation, or do I mean condition? where the hose between tank and pump deteriorates, allowing air to be sucked in and the pump then just keeps going.
One might expect this to also show up as a leak but the rubber hose has enough resilience in it to seal the leak / split enough to prevent fuel from dripping out when parked, even though the pump will pull in air when it is operating. It does make it hard to trace the fault.
GuyW

Guy & Les
Had exactly the same symptom on my 1500 last weekend - the pump needs to suck to prime (not sure where the Frogeye pump is mounted but I suspect theres a lift involved?)

Any air leak on the suction side will stop it priming and then pumping, and as guy says the hose may act differently when under suction than when full of liquid

I'd check those new flexis for leaks/tightness
timmyk

Les,

Fill the tank up and see if the problem goes away. The pick-up tube in the tank can get damaged and result in air being drawn in when the fuel level is low, also check the steel pipe out of the tank is seating correctly as it also functions to seal the internal tank tube into the tank outlet boss. If the fuel level is above the outlet boss and the problem goes away you have an issue in the tank or the outlet boss.
David Billington

This might be really dumb so try not to be too harsh correcting me!
I have no real familiarity with the SU pump but as I understand it, it's a reciprocating pump so the supply polarity shouldn't matter - if it works (reciprocates) it should pump.
Forgive me, but are the hoses the right way round? You're not trying to pump fuel *into* the tank are you?
Greybeard

Thanks for the suggestions folks, but this episode started when I renewed the hoses so I don't think they are the problem. They are good and tight, and the right size. And yes they are the right way round. The pump does work, it just doesn't stop when the carb is full. Well I don't know if the carb is full, but the engine starts and runs OK. I still think it's sucking air through the inlet valve.

The broken pickup pipe is a valid point. I had this many years ago and catheterised it with a length of Bowden cable outer down the middle (my son's suggestion - he was at med school at the time). No problems since, but I will check it. It is of course impossible to repair the pipe.

Good choir rehearsal BTW.

Les
L B Rose

Apparently not impossible. Had to search a while but I dimly remembered this from a few years ago. It might have been Prop who mentioned it, or maybe not.

http://www.mgexp.com/forum/mg-midget-forum.3/pin-hole-in-pickup-tube-results-are-in.1108573/

IDK, it might be useful.
Greybeard

As it just happens , I had this very issue on a friends MGA a while back--
Is your fuel pump mounted correctly with the outlet above the inlet and if it's an earlier pump ,with the filter,, at the bottom
On the mga the pump had been mounted upside down causing an airlock in the pump, it took some finding as the old pump that had been recently replaced with this ticking one had also been upside down
If you go for a long drive or take the fuel line off up the front and run the fuel pump for a while it will eventually bleed the air out of the top of the pump and it'll be ok, as in stop ticking BUT better off mounting it correctly if it's wrong
Any chance of a pic of how it sits-------
William Revit

Thanks Grey, I had no idea the pickup tube was removable. I'll give that a go. I just replaced the seals in the pump and, you guessed it, no difference.

Yes the pump is the right way up.

Les
L B Rose

In fairness I've never tried it either, but it makes sense to me. After all, someone had to put it in there to begin with. Good luck Les.
Greybeard

I just tried another test. Inlet hose in jug of petrol not the tank. Worked perfectly once primed. So it is most likely the tank pickup. Getting the pipe out of the tank is a challenge.

Les
L B Rose

Test the tank outlet first. Gravity and a length of hose would do at first, then on to low pressure suction/syphon. Always best to check, double or even treble check first. (And test the testing equipment before each test).

Nigel Atkins

Les, I don't think my problems quite match your symptoms but I've hit a couple of fuel flow problems in the past so I'll add my two penn'orth just in case it's useful.

The first fuel starvation problem turned out to be sediment blocking the pick-up pipe in the tank itself - I found that when I sucked instead of blowing when I was checking if the pick-up was clear!

Occasionally, I get a fuel surge problem when going round a long right-hand bend or roundabout with the tank only a quarter full. The fuel sloshes to the left and exposes the pick-up which sucks in air. A long bend gives sufficient time to suck in enough air to create an air lock where the pipe runs over the axle. With the pump running, pressurising the tank via the filler cures this and you can tell as the pump goes quiet.

Mine's a Facet pump fitted to replace the SU before I finally tracked down the sediment problem. I don't know if I would still have the air lock problem with the SU.

Colin
C Mee

I am having a merry time with this. I pulled the pipe out leaving the filter in the tank. I had a bit of cunifer tube that fitted inside the pickup pipe, and glued that in with Araldite Metal. Then I found I could not stop the pipe from rotating inside the tank when I tightened the brass union. At least that's what I thought was happening. Pump still sucking air. Nothing for it, off with the tank. But first the panhard rod had to come off, followed by 2 days dealing with the rampant corrosion of most parts. All restored now with 2 coats of stone chip. I took the opportunity to weld in the longer studs that I had to use for the panhard rod - they were only glued in before as I didn't fancy welding an inch from the fuel tank.

I found the pickup pipe could rotate because the clip inside the tank is bent away from it. I can't see how this can happen other than at the factory while the top is off the tank. So I restrained the pipe with a wire hook through the gauge sender unit hole, and screwed in the union. I had the sense to check the tightness of the pipe before I put the sender unit back. You guessed it, it flaps around. This is why the pump sucks air. I certainly could not get another turn on the brass union, for fear of stripping the thread. I wonder if there should be a fibre washer. My official parts book doesn't even show the brass union so I have no idea. I might try a fibre washer tomorrow if I can get one the right size.

The lengthening of the pipe is probably not necessary as it goes to the bottom of the filter anyway. The latter though is no use as there is a hole in it, and there is no possibility of putting it back on the pipe.

I just looked at the Moss parts diagram. This is different from my car, as there is no 90 degree brass union, the metal fuel pipe goes straight into the tank. Maybe I should change to a male fitting with an olive and ditch the union.

Les
L B Rose

Well, that's interesting. Well done so far! Without seeing the hardware in front of me it sounds to me like the solution you suggested is the way ahead. So long as a union can be sealed satisfactorily to the outside of the tank it sounds like a stainless steel through pipe in a Swagelok fitting would be the cure.
Perhaps an external inline filter would be a good idea too.
Greybeard

Les,

The original had a brass cone soldered on the end IIRC and the nut pushes that into the pick-up pipe to seal it to the tank boss. I fitted a compression union years ago and had air pick-up issues like you, took ages to figure out what the problem was. Changed it back to standard and all problems went away. Did you fill the tank up as I suggested earlier as that gives a good indication of the problem as it goes away until about 1/2 full.
David Billington

Grey, I have a filter on the carb end. I'm not sure about a Swagelok fitting as the end of the pickup pipe is flared and I really need something that goes into it - like an olive. Does anyone else have this 90 degree brass union arrangement? It was on the car when I bought it 40 years ago so I thought it was standard. But there is only a butt joint to the pickup pipe and I think it should have an olive.

David, no I didn't fill the tank right up as then I would have had to drain it and I only have 3 x 1 gallon cans!

BTW the tank is spotless inside as I cleaned and sealed it when I did the rebuild.

Les
L B Rose

THe Su AF200 series can lift 18" so should be able to such fuel out the tank as long as the tank inlet is covered.
Graeme Williams

Les, this is a bit of a wild shot, but: The pump will continue to tick if the carb float needle valve doesn't seal. This would normally result in fuel running out of the overflow. But, if the choke is out then the jet is lowered and fuel can flow through from the carb so the float chamber never fills enough to properly close the needle valve. The surplus fuel then drains directly into the engine so may not be apparent. It doesn't take much to get this happening. Car on a slope with choke fully out will do it.
GuyW

Les,

The item I refitted which cured my problem was item 23 here http://www.msc.parts/contents/en-uk/d373_1275cc_-_Fuel_Pump___Fixings.html image http://www.msc.parts/contents/media/l_aca5129.jpg it solders to the end of the tank outlet tube. I fitted a compression fitting, IIRC the tank thread is 3/8" BSP, but then I had the problems as you do a bit over 30 years ago. It seemed a good idea at the time but when you understand how the OE fitting works is doesn't. The olive idea might work but my experience says it's not ideal as the outlet tube is the same size as the pick-up tube so the olive is not constrained as it normally is and may not seal well.
David Billington

Guy, that's a good point and I will check the needle valve.

David, I can't see how that nipple can solder to the outlet tube. Do you mean the pipe inside the tank or the one from tank to pump? Here is what my pickup pipe looks like. The flared end goes right inside the threaded socket on the tank front wall. Also showing the 90 degree union.

Les


L B Rose

Les,

The nipple solders onto the tube from tank to pump and the nut pushes it against the internal tube flare to seal it to the tank boss so it doesn't let in air. The compression fitting elbow isn't screwing far enough into the boss to seal the internal tube.
David Billington

Les
This is what David is refering to

The tapered nipple is soldered to the pipe and a threaded 'ram nut' pushes it into contact with a similar taper within the fixed tank boss.

R.


richard b

Les, I did say my suggestion is a "long shot". Although he carb chamber will drain through the jet tube if it is in the lowered, choke out, position, I suspect that this loss would be quickly overcome once the fuel pump started operating, and it would then fill up the chamber and should at that point close the needle valve and stop clicking. Still worth checking though.

I do know one should never leave these cars parked up with the choke pulled out as fuel will then find its way into the engine, eventually diluting the oil.

Regarding the tank conection, there has long been a problem of mis matched parts with the threaded boss on some of the tanks being too deep for the thread length on the tube nut. The result is that the shoulder on the tube nut tighens onto the face of the tank boss before the soldered-on olive gland is compressed. Check your thread lengths! If you cannot get the correctly matched tube nut, then you may get a satisfactory seal by wrapping some plumbers' PTFE tape around the pipe and olive gland to bulk it up
GuyW

Les,
this is what David means, this tank outlet pipe has the nipple/olive on the end. -
https://www.moss-europe.co.uk/fuel-pipe-main-feed-cpp7148.html?assoc=419977

BUT - this is the olive that shows for the Frogeye

https://www.ukmgparts.com/product/mid-midcat-1-submid9-fuel-tanks-pumps-pipes-fixings/fuel-pipe-olive-midget-21a2771

http://www.somerfordmini.co.uk/eshop/index.php?main_page=product_info&products_id=13305
Nigel Atkins

ETA: I ran out of time to alter my post (phone call interruption)

I'm not sure if the Somerford Mini part is correct based on the price and the drawing.

And AH have this, which again I'm not sure of as they use different part numbers and not image or illustration. -
https://www.ahspares.co.uk/austin-healey/sprite/fuel-system/olive-fuel-pipe-tank-to-pump.aspx
Nigel Atkins

If the tube nut is to short as Guy has noted as a potential problem with faulty parts, (other than replace it) another 'work round' would be to slit a very short piece of fuel tube, open it a little and pass it over the fuel tube behind the nipple and reclose it around the pipe - this should compress up enough to allow the required seal.
richard b

Sorry I'm running out of step with everyone else (as usual) but will carry on with my (alternative?) theme.

Les,
I'd bin that elbow (give it the big 'e' :) ) and return to original, that is assuming (always dangerous) that you have an original style Frogeye tank with original fittings/union, and use original olive and nut/union fitting.-

21A2770 - https://www.ukmgparts.com/product/mid-midcat-1-submid9-fuel-tanks-pumps-pipes-fixings/nut-midget-fuel-pipe-21a2770

21A2771 - https://www.ukmgparts.com/product/mid-midcat-1-submid9-fuel-tanks-pumps-pipes-fixings/fuel-pipe-olive-midget-21a2771
Nigel Atkins

Success! You will all say this is a bodge, but I trimmed down a fibre washer and fitted it between the pickup pipe and the elbow. Having found the pipe was now tight, I removed the elbow again to check that the washer was in place and it was. All back together now and the pump works fine. No leaks of air or petrol. Later I will probably change to the correct parts as you guys have kindly explained. There was a brief burst of swearing when I found the battery had gone flat overnight. Bloody radio keeps turning itself on. Enough charge now to start the engine so I don't need a lift to choir rehearsal tonight.

Thanks again for a wealth of advice.

Les
L B Rose

Les,
well done.

It's only a bodge if it doesn't last 12-15 years, that is a temporary repair and can be forgotten about until you rediscover it.
Nigel Atkins

Good to hear Les.
BTW if your radio is a modern one, check to see if it has Bluetooth enabled. The dang things can switch themselves on mysteriously if someone passes close enough with a smartphone in their pocket.
A girl I knew with a BMW was puzzled for ages why her radio was on in the mornings. Her usual parking spot was near a bus stop and it was caused by bystanders phones. Took a bit of figuring out, but she just disabled Bluetooth and the problem went away.
Greybeard

Les,

Good to hear you have confirmed the issue, I had wondered if a lead or soft copper seal of the right size might do it. A quick look seemed to indicate that a fibre washer may be OK with hydrocarbons but I would keep an eye on it as I know someone that used one on the sump plug on their Mondeo as they were too tight to get the proper seal and it failed in less than 10 miles allowing the sump contents to drain out, fortunately they had just parked when the sump plug dropped out, that may have been oil and heat related.
David Billington

Arrrggghhh!!! Bluetooth. I had forgotten about that. I did use it briefly to link music on my phone but find a micro SD card much more convenient. Sorry for the pollution of this forum with something modern.

Les
L B Rose

I have now upgraded to the soldered nipple and nut. Much better. It doesn't try to rotate the pipe when screwed in.

Les
L B Rose

This thread was discussed between 01/10/2019 and 15/10/2019

MG Midget and Sprite Technical index

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