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MG MGB Technical - Fuel Problem

Hi there,

Sorry if this has been answered before, but I've just bought my very first MG.

It's a 1975 BGT "Jubilee".

The problem is that she will start and run (just!) but if I drive off, she coughs and splutters to a halt. If I then wait for a minute, the ignition comes on, the fuel pump makes a strange noise and she will start again, only to conk out 50 yards further down the road.

Any ideas?

Keep it simple guys, I know a bit about engines but not a lot! Any mentions of "the crossbeam being out of skew on the treadawl" or other over-technical nonsense will result in a slap!
M J Paull

Ah! Old Chap,

Such a simple problem, but so many questions to arrive at the solution.

Has the car been sitting for any lenght of time --was it in operation when you took it under your wing? (Fresh petrol there)

Take a look at all vacumn/air hoses and clamps on the engine.

Take the bowl off the carb/s and cleck for water, debris.

Change the petrol filter.

Do you know when the last tune-up was?

Check the distributor cap for dirt/moisture; clean the rotar with a very fine abrasive cloth - emery or sand paper; check the spark plug wires for dirt/grease and that they are not close to any groundings -- (like touching the engine block.

There's some other things to consider -- like electrcal but this would be *my* let's look at these first.

Keep us posted on pregress.
glg

Hi.

"the ignition comes on, the fuel pump makes a strange noise and she will start again"

Do you mean that the ignition light (the red one on the dash) suddenly comes on of it's own accord ?.

If so, it suggests that you have a poor electrical connection in the circuit fed by the ignition switch.

If the crossbeam was out of skew on the treadawl the engine would run but the car would only go backwards on Tuesdays.


Don
Don

Back again!

Right, as far as I'm aware, the car was in regular use up till march this year. That's when the tax expired and it's only just out of MOT.

The ignition lights always come on. The first time I try to start her, the fuel pump doesn't make a sound, the engine fires up but can't seem to keep going. The throttle needs to be pumped to keep it running. I drive off round the corner, she cuts out like no fuel is getting through. I wait, the fuel pump does it's thing, then she starts like there was never a problem, only to do the same thing 50 yards further on.

I don't know when she was last tuned, but it's on the list of things to do.

If it helps or makes a difference, I have been reliably informed that the carbs are SU's with K&N filters.

Thanks for the feedback so far and I'll keep you posted on the outcome. I'm off to have another look today so watch this space.
M J Paull

Hi.

It is normal for the fuel pump to give a few clunks (a bit like someone rapidly knocking a door) when you first turn the key, as the pump fills the carb float chambers.
It seems that your pump may be sticking.

The pumps do sometimes suffer problems with their contacts, which a calibrated newtonian pulse (ie hit it) often cures.

Don
Don

Fuel pumps rarely "stick" what you probably have is burned out or dirty contacts inside the pump.

When you first turn on the ignition you should have a healthy burst of clicks from the pump which slow down and stop. The engine should then start and run normally.
As fuel is drawn from the carbs the pump will pulse to replenish the bowls.

Look in the boot - there should be a square steel cover over the pump which sits half in and half out of the boot.

Remove the two screws holding the cover to the panel and pull off the wire from its contact, undo the nut holding the contact to the pump - it also retains the black plastic pump top. Pull the cover off the pump and peer at the contacts - if they (and the pump) are relatively new looking, clean the contacts by drawing some ordinary paper between them - if the whole set up looks old and dirty, just buy a whole new SU pump - these will give years of troublefree service. Go for the electronic sort and there are no points to worry about.
Chris at Octarine Services

Back again!

It was the fuel pump!!

The car started first time, and I even went for a spin!

However, it soon conked out again so I started my diagnosis. The plugs were in excellent condition. The previous owner had fitted Bosch plugs with 4 electrodes each and they were in good nick so I left them be.

I then decided to give the fuel pump in the boot a whack and hey presto, it worked!

It's still a little tempremental, so I'm on the hunt for another one. I can only see one wire coming out of the top of it and I'm hoping it's a bog standard BL part. Any suggestions on where I can get one?

Watch this space as I'll probably be asking loads of other questions such as what the hell is that noise coming from the back end when I corner?

Cheers folks!!
M J Paull

Paul - Your pump is a AZX 1307 SU pump (standard) and is available from any number of sources that handle MG parts in you area or can be ordered directly from Burlen Fuel at: http://www.burlen.co.uk/ . As Chris stated, a new standard pump will give you many years of faithful, service a all electronic version, even longer. While I am a great advocate of fix it yourself, the fuel pump is not an item to be done by the neophite. To get it set up correctly, is a pain unless one has a test stand and I suspect that many of the "problems with SU fuel pumps" are self inflicted by people trying to affect repairs or overhauls themselves.

Before those of you who regularly repair their own pumps flail me and throw me to the fish for the above remark, I know that tehre are a large number of you out there who have successfully repaired or overhauled your own pumps, but I have also gotten many sorry remains of pumps that people have tried and failed to get repaired themselves. So if you are good at repairing electro-mechanical things, by all means, go for it, but if those things leave you scratching your head, you will avoid a lot of short term and long term frustrations by just replacing the bloody thing.
Cheers - Dave

PS. Paul, there is one other electrical connection to the point to the pump. On the pump body (outside the trunk) there is a ground wire connection. Be sure to get that wire back into place or the pump won't run.
David DuBois

This thread was discussed between 19/06/2004 and 20/06/2004

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