Classic cars forum & vehicle restoration.

[kimchris]

Hi all, the 6v su fuel pump which came with the heap of junk we will eventually call a car did not work when tested. I assumed it was the points and fitted a new set. I have the manual for su carbs and pumps and followed the setup instructions exactly. On re assembly the pump still does not work, however, with the 6 screws removed and the front off it works fine. Re assemble the front end with a couple of screws tightened and it does not work. I have tried screwing the diaphragm out a turn at a time but nothing. Every time the front is tightened the pump will not work. I am wondering if either the coil is too weak or perhaps the diaphragm is not flexible enough. It has been stood an unknown number of years. Any suggestions?

[Phil - Nottingham]

it could be weak but if the diaphragm is not slack when the screws are tightened especially if it is dried out and stiff it will not flex and pump. Arrange it so its pulled in when tightening up the screws - it usually works
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Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2

[peter scott]

Sometimes the fixed (springy) contact fails to make a good connection. If the contacts are clean see if you can induce some life by applying a little gentle pressure to the springy contact.
If this works then give it a slight bend inwards.

There are later versions that have double contacts and it is possible to substitute this system for the older single contact scheme. This makes them much more reliable and you can hide it under the original cover.

Peter
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http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[goneps]

If you have the old-fashioned type of diaphragm assembly which can be dismantled and comprises two rubber membranes, you need to place the thinner membrane at the front, ie. towards the coil, and therefore the thicker towards the valve body.

The official instructions state that the diaphragm rod should be screwed in until the rocker points mechanism stops 'throwing over', then unscrewed one hole at a time until it just throws over; from that position it should be backed off a further 2/3 turn or four holes. In my experience this is not enough, and after a week or two the pump will occasionally stop working. Consequently my preference is to back off one full turn (six holes). When testing the throw-over action the diaphragm centre should be pressed with a slow and progressive action—don't jab it.

The instructions also advise that the rod be pulled up to tension the diaphragm while tightening the six screws.

In fact, rather than six screws there should be five screws and a stud (see picture). The latter carries a 2BA nut, providing a terminal for an earthing wire. Without this the earth is uncertain; you might get away with it for years, as I did, but eventually the pump will become erratic in the absence of a proper earth.

Richard

[TribalElder]

A well written and informative response... thanks
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Ian from Oz

It's hard to run like an Emu
When you are girt by Numbats

[kimchris]

Thanks for the info everyone.

Sounds like tensioning the diaphragm before tightening the screws might be worth trying. I didnt do this.

By the way my pump has 6 screws and a separate earth screw.

[kimchris]

I had another go at my fuel pump and this time I inserted a 2in round head nail under the points therefore pulling the diaphragm in towards the coil. I would estimate that it lifted the points about half of their travel. Then screwed the 6 screws to hold the diaphragm and front end. Now the pump works fine.

Andrew

[NONORT]

I have only just caught up with this thread. I got feed up with buying sets of points for my moggy and converted it to electronic with a kit from Burlen fuels. No connection with Burlen just well pleased.

[goneps]

Or you can simply add a zener diode, which stops the points arcing:



No doubt a somewhat cheaper alternative.

There are some rubbish points out there. I had a set (made in Australia) that lasted only 500 miles. Refitted the 1936 originals, and they went on for several more years. Much prefer the single points, myself.

Richard

PS. Can anyone tell me how to post a smaller Photobucket image? I've reduced the size in PB but it still comes up huge in this post. Thanks. R