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MG Midget and Sprite Technical - Fuel delivery problem

1500 midget 1977
Went out last week, yards from home (fortunately) loss of power, cough splutter. Stopped, handbrake on. Tried to rev it, virtually no power, then the engine died.
Initially I looked at the electrical/ignition side, all appears to be OK, good spark etc.
I have now looked at the fuel. The tank is ¼ full.
I took the supply pipe off to the carburettor, turned the engine over a few times – no fuel came through.
I took the “out” pipe off the fuel pump, turned the engine over a few times – no fuel.
I took the supply pipe off, got my daughter to listen at the filler end, blew down the pipe, definite gurgling bubbling noises.
I connected a clear bit of hose to the fuel delivery pipe and used a reverse acting inflatable toy pump and it sucked up fuel from the tank with no problem. So there didn’t seem to be a blockage in the fuel line.
In between this I did take off the lid to the fuel pump. I was surprised to find that there was no gauze filter.
I have now taken out the pump.
I thought I would just try a little test with some bits of hose and a small reservoir of fuel. Using the priming lever, I gave it a try and it pumped fuel absolutely fine.
I assume that if it pumped fuel with the priming lever, then the pump is OK – all bar the missing gauze.
Not sure what to check now though!!
Nigel Axtell

Possibly a split diaphragm in the fuel pump. Separate the two halves by undoing the 6 (or is it 8?) screws. When this happens the pump may still appear to work when tested manually, but in use it is unable to create the pressure to supply sufficient fuel especially when you rev the engine or are driving up a hill.
Guy W

Nigel, a couple of thoughts spring to mind if you haven't found any explanation...

Firstly - I wonder if the fuel tank has some scale ( rust flakes etc) - I had a mini which suffered similar symptoms to your description - I eventually worked out that it would run until the pick up pipe gauze in the tank was coevred in scale flakes and would block up and cause fuel starvation.. - solution was to flush tank and clean out the scale.. - also fitted an in-line filter to catch any small stuff - as its not very good for wear...

I am not sure what the pick up in the midget tank is like - but could explain all your symptoms I think.

Also - I have heard of tank vent getting blocked - usually in filler cap /neck - when this happens vacuum can cause fuel starvation I think ..

You can hear a hissing/air rush noise when you release the filler cap if you have this happen .. To rule this out try running without a cap ?

Good luck - its a really annoying thing to happen - as with my Mini it only happened on a low tank level - although this took a while to find out.... After stopping in some incovenient places I resolved to make a logical part by part investigation as you described above - eventually found the scale problem...
John Barber

Id to the above... And all are good.. but check the points, they can get a bit gummmy if left for a long time esp in wet weather
Prop and the Blackhole Midget

This thread was discussed between 27/08/2012 and 28/08/2012

MG Midget and Sprite Technical index

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