Fuel pump problems


My 68 Series 1 is running fine on the RH tank but splutters and stalls within half a mile if I switch to the LH.

I think the issue is with the pump. The right clicks away with the ignition on, the left doesn’t. There is a feed to both. When I test the LH pump with a multimeter it makes an audible alarm when the dash switch is selected to the RH tank…

My electrical knowledge isn’t great but I suspect a capacitor problem, something has burnt out and is shorting…?

I have removed the LH pump and attach some photos. It is different to the RH pump. The RH pump is a single assembly… the LH pump has a 2” barrel attached to the bracket, with a wire connected to one of the feeds to the pump. I think this may be the capacitor and potentially the source of my problem?

Any suggestions as to what to do? The points are a little charred and I can clean them off if that seems to be the issue. But does my electrical testing suggest this is a capacitor issue and that I am better swapping out the pump?

I suspect the RH pump has been changed at some point and is a different design which is why it doesn’t have this separate barrel connected to it (which as I say, I think is a capacitor).

Thanks for tips! East enough to get a new (negative earth?) pump and swap in if I have to.


File (sand) the points and throw the capacitor away. The large silver one outside the pump, not the black one.
Never a need to replace the entire pump, if it’s not clicking there is a reason for it and whatever the issue is can be repaired.

Thanks David - I shall try that!

Good luck - if it then clicks but not fast enough, split the pump and adjust the diaphragm by turning it in or out until the points mechanism throws over nicely. Will need a few attempts until it is just right.

The capacitor almost certainly not the problem. You can leave it disconnected temporarily to diagnose the problem.

Most likely the points are corroded and not enough voltage/current gets through to the pump motor winding.

This is exactly why I developed SU fuel pump electronic upgrade

Since you have one good pump, all you need to do is work out what the differences between them are and that’ll reveal where your problem lies.

kind regards

It is a nice long term upgrade but let’s lkeep it simple for now, shall we?
The pumps last forever and rarely go bad, usually after many miles.
Comparison to the good pump is the way to go!

WAG. The capcitor is not reqired fro fuel pump operation. It is to eliminate noise in the radio. Elimaiting it may or may not result i radio noise. If shorted, it may effect pump operation. \I do not think that ump work. any mileage you get after seitching to it s from te fuel in the carb bowls.

i will leave the chrred point issue to others. but, will comment, tyhat is a possible case of failue.\Crl

Thanks Carl. Yes, I guessed the distance I was getting was from the bowls and that from the moment I flicked the switch I was on borrowed time!

I shall try cleaning the terminals first…

David, thank you - I filed the terminals on the rocker mechanism and the contact blade. The photo shows one contact after filing, against one showing how it was originally.

Pump working fine after a 6 mile test drive.


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I‘ve got a pump off ebay that was sold as defective, the contacts are seriously worn, almost down to nothing but I cleaned them and that pump is a spare now (not that I need one), works perfectly and it would still be reliable for a few months or a few odd jobs. All that was needed was a bit of filing and a little bit of adjustment.

The distance you got was from the float bowls. Happy it worked out!

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