SU fuel pump

That sounds very likely. You should be able to get a kit to rebuild this pump (try

If it is an old diaphragm I would change it anyway as they are not always proof against some modern fuels, though if the thing is leaking I would expect to find traces of petrol around the hole. Clean it and rub some chalk round it. That should show you. Cleaning the valves under the outlet union would be a good idea as well.

Ron Robinson

Thanks I tried that the valves are clean as and no leakage. I cant find any traces of petrol true the rubber and the pump works ok when I put a short hose on it. But when I put a 2 meter hose on it it cant pump up the petrol from the a can it seems to suck air somewhere I tightened up all the screws but that did not help.

Hans

pumps fuel if I

is leaking? Or

are not always

leaking I would

and rub some

under the outlet

cant find any

put a short

up the petrol

all the screws

It would probably help, if you told us exactly how the pump behaves, rather than just telling us it can't pump through a 2m hose. What it does, gives a guide of where the problem might be. Does it race, slow down, stop. What? If it races, and the diaphram is not leaking, it could be sucking air or the valve/s are not sealing. Otherwise, maybe the solenoid has a short cicuit reducing it's effectiveness, or it could be the core that's sticky. It's some time since I worked on them, but I've never failed to sort one out. There's a lot that can go wrong with them, but most faults are easily fixed Mainly just by cleaning and adjustment. Blocking the drain hole should make no difference at all. IIRC, it's only purpose is to reduce the possibilty of petrol from a holed diaphram reaching the points. It's not needed pump escape

Yes. If the membrane is leaking then the pump will leak and will probably run continually rather than not at all. The more likely explanation is that the diaphragm is just stiff with age or that the springy contact is getting tired and has bent down a bit. I suspect the former case. The shaft doesn't come back quite far enough for the contact mechanism to flip over. The extra pressure caused by blocking the air vent makes the difference.

The answer is to renovate the diaphragm if necessary, or adjust the contact mechanism by winding it back a turn or two on the shaft. Also make sure that the springy contact is correctly positioned to make contact with the moving bit.