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MG Midget and Sprite Technical - Engine Dying & Fuel Pump going mental

My car has developed an irritating habit of dying on me.

So here's what happens.

Pull out choke
Starts perfectly
fuel pump over pumping
Start driving runs great
Choke in
Still runs
Fuel pump still over pumping
Feels like the engine is running at half power
As you slow up it dies and struggles to restart
Fuel pump still pumping like mad.

RAC said the choke was sticking open causing the engine to flood.

After it broke down it, it ran great for 30 miles to get me home, but it is doing it again tonight. Grr.

Is it choke or a dodgy fuel pump over pumping?
Stephen Frew

more likely the outlet joint on the tank letting air into the petrol line even though it wont let petrol spill out

I have THAT tee shirt

check the outlet, have you had either a new tank or a new pipe connection lately?

Is there a fuel filter inline before the pump which may be blocked and collapsing?

Look for yourself at the choke, get a lovely assistant (mandatory in these cases, so you just have to bear it...) to pull out the choke while you look at the linkage on the carbs then ask said LA to push it back in, if it's sticking you will see it stay where it got pulled to

or not
bill sdgpm

Agree Bill's diagnosis,

OR: you have a sticking carb inlet valve - either wear, a bit of dirt lodged in the needle valve so that the float isn't closing off the fuel supply. Pump just goes on clicking and high fuel level causes ultra-rich mixture and engine struggles to run properly.

Remove the float chamber tops and the valve needles. Let the fuel rinse through the valve to get rid of any crud but also check the tapered point of the needle for signs of wear and replace if there is any sort of ridge or mark showing.

Guy
Guy Weller

if there was that outlet joint, would the plugs still read rich? it seems like knowing that would make it a tad easier to diagnose.
Seth Brecklin

Thanks guys,

I did just get a new fuel line.....about a month ago.

I guess that fills out my Bank Holiday Monday!
Stephen Frew

New fuel line could point to Bill's diagnosis - or fitting it could have dislodged dirt in the tank / fuel line and caused the needle valve to stick open.

Check under the bonnet with the engine running and pump ticking like fury to see if the carb overflow is running out fuel, or if there is an unusually strong smell of fuel around the carbs.

Excess fuel running into the carb manifold & cylinders can cause engine problems. It washes lubrication from the cylinder walls causing them to wear rapidly and also dilutes the sump oil so the bearings can suffer. So don't "put up with it" for too long!

Guy
Guy Weller

When you say the fuel pump is over pumping, is it pumping fuel or air?

I had a problem with my MGB where the fuel pipe between the tank and the pump had a tiny hole in it at its highest point, as it followed the curve of the panel above the axle. It didn't leak fuel but it did allow air to enter the fuel pipe/pump, preventing the engine from starting. It took some finding.

Assuming that it is pumping air, I concur with Bill.
Dave O'Neill 2

Stephen,

I've had the problem with the fuel connection at the tank letting in air as well. Easy way to check is to fill the tank with fuel, the problem only occurs when the connection is above the fuel level. The issue is that the union nut on the fuel line pushes the olive into the tank pick-up tube flare and forces it against the back of the tank boss to create a seal, if it doesn't then air leaks in from the tank when the fuel level is low.
David Billington

I recently purchased a new tank from Moss and a new pipe with the fitting from VB. I was doing a test fit a couple days ago and noticed that even when just hand tightening the nut that it comes very close to contacting the outside flat of the tank bung before the tube seems to make contact.
Giving some serious thought as too what to do with this latest challenge.
tomshobby

If your set up is using a nut and olive, on solution would be to get a nipple (Moss P/N 376-415) and solder it onto the end of the fuel line (after removing the olive first). Another (less eloquent) solution would be to file the end of the nut down. Cheers - Dave
David DuBois

Had exactly the same problem today, only to eventually find that the hose from the tank to the Facet pump was cracked, letting air into the system, so the pump was banging away like a good un, but no fuel. One way to see if this is the case is if the pump slows down if you block the pipe before the carb, indicating it is still pumping, but just air.
Neil Williams

Looking at the evidence why not agree with the RAC man's diagnosis?

He said the choke was sticking on (not uncommon) and would cause the symptoms you describe. sounds like when you called for him he manually pushed the choke off and you were able to run the car home perfectly.

Now I suspect you have used the choke again and again it has stuck on!

Try starting the engine and then after a couple of minutes stop the engine and from under the bonnet with the choke pushed off, push the 2 jet pipes up into the carb. If the choke has stuck on you will feel one or both of these jets push up slightly.

Then run the car again without touching the choke cable, if it runs great then the jet tubes need to be loosened off so that they return up when you release the choke cable.

This is the kind of thing that happens frequently with these carbs.
Robert (Bob) Midget Turbo


I had the same symptons only last week and as i had just taken the carbs off to clean and put a new heat shield on was sure that I had messed something up then i noticed that one of my jet assemblies had dropped from its linkage as soon as i pushed the it back to it's proper possition the carbs work just fine.

if this is the case then you would not notice from above as the choke linkage still looks as if it is working.

regards

Douglas

df mccabe

This thread was discussed between 30/05/2010 and 06/06/2010

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