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MG MGB Technical - Fuel Pump

My fuel pump does not work on 1977 MGB.
Could this be due to a bad fuse?
Any way to test for this?

Thanks

Bill Chandler
W Chandler

Not fused from the factory, but adding one is a good idea.

If it's an original pump it will have points and these do fail eventually from one of two causes - either oxidisation where the pump makes no sound at all when you turn on the ignition, or from spiking and pitting (similar to ignition points) where it just makes a single click each time you turn on the ignition. If there is a bad connection in either the 12v or the earth supply it will also make no sound.

As a 77 the electrics end of the pump is in the boot and quite easy to get at. Remove the black metal box cover that should be there to expose the end of the pump. You should see the 12v connection, so first is to use a voltmeter to test for 12v from there to a good earth elsewhere.

If you see that test for 12v between that terminal and the body of the pump, which you should be able to get at under the large rubber grommet you should see. You should see 12v again, if not then perhaps the earth is bad, which comes from a spade terminal underneath the car and goes to one of the number plate bolts along with several other wires. More information on those aspects here http://www.mgb-stuff.org.uk/pumpmount.htm#2

If the pump has a good 12v and earth then it's probably the points, more infio on cleaning and resetting those here http://www.mgb-stuff.org.uk/pumpr.htm
paulh4

looking for a little help.

1978 mgb starts then quits.over and over. new tank and pickup. new fuel pump. new SU carb(single)have 12 volts at the pump. have 2.5 lbs pressure at the carb.

suggestions?
dhh dennis

looking for a little help.

1978 mgb starts then quits.over and over. new tank and pickup. new fuel pump. new SU carb(single)have 12 volts at the pump. have 2.5 lbs pressure at the carb.
suggestions?
dhh dennis

the weird part of this is: if i put a squeeze bulb in line and have someone keep squeezing the bulb it runs. as long as the bulb is squeezed. wth?
dhh dennis

Take the fuel feed off the carb, direct it into a container, and turn on the ignition. It should deliver at least one Imperial pint per minute in a continuous series of pulses with minimal bubbling. If it does that the pump and supply is OK.

In which case it could be the carb float valve not letting enough fuel through until it gets extra pressure from the squeeze bulb.
paulh4

the SU is new out of the box. there were no instructions from LMC or Victoria British on float valve adjustment. is it simple?
dhh dennis

i do thank you for your help.
dhh dennis

Eliminate fuel supply first. Static pressure is not a good enough test, you need to confirm the flow rate is adequate.

What type of SU carb - HS or HIF? Whilst it can be described here - at length - you really need a manual. You can Google for it, there are videos from John Twist and Moss, and descriptions from SU Burlen - https://sucarb.co.uk/technical-h-type-carburetter-float-chamber for HS and https://sucarb.co.uk/technical-hif-type-carburetter-reassembly for HIF.
paulh4

There isn't any adjustment for the float valve. In your case, make sure float valve needle isn't sticking - they sometimes have a little viton tip that can stick in the brass housing in the float bowl lid. The foregoing applies to an HS4 - you may have a later carb and I'm not sure of the arrangement on those, other than the principle holding true for any carb.

Peter Allen

There is to the float which controls the valve - or at least a check to ensure the level is correct. Not all floats are adjustable as such, which is when you have to use spacer washers on the valve itself.

Sticking or dirty valve can affect both HS and HIF as the valves are fundamentally the same.
paulh4

dhh dennis,
more information and/or photos would help with others helping you. Your car and it's fittings and parts may not be as standard or factory original.
Nigel Atkins

This thread was discussed between 26/08/2019 and 26/09/2019

MG MGB Technical index

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