SU Fuel Pumps - they are not inherently unreliable!

The original SU pump is very reliable for about 12 - 15 years.

Once it starts to falter, overhaul it and it will be good for another 12 - 15 years.

The SU pump only ever had one problem - that when it did get old and tired and falter, it would respond to a tap (which eventually becomes a hit as it gets worse) and start working again. Thus, people would not get around to overhauling it (just give it another hit), yet mutter about the unreliability (hit it again) of it every time they had to crawl under the car and HIT IT. So was born one of the great urban motoring myths! Of course it was unreliable then - it was worn out! It's a bit like running tyres worn through to the cords and wondering why you lose the air so often!


A new set of points and a new diaphragm (include new valves for a belts and braces approach), all correctly adjusted as per the workshop manual, and it will run happily for another 12 - 15 years. As simple as that!

Finally, (for what it is worth) avoid the electronic SU clones - I get a lot of feedback about them failing.

If your pump operates too rapidly, There are only five possible causes:

  1. No petrol in tank, or faulty pick-up
  2. If the system has been opened up - the pump is not yet primed (quite common) This can happen when it is working against air pressure and the air pressure confuses the pump's valves) To check, disconnect the outlet hose of the pump from the pipe going forwards to the engine and operate the pump until petrol comes out the hose. If air comes out initially, this is likely the problem. Reconnect and the pump should then operate for a while until filling the carbs, after which it should slow to a click every 5 - 10 seconds as per normal.
  3. Air weeping into the intake line at a joint (this is possible even though there is no petrol weeping out). Double check all joints for tightness.
  4. Grit under the valve in the pump (sucked through from the tank) Clean out tank.
  5. Faulty valve in the pump. Renew valve.

Not convinced? Here's something to reflect on:

When electronic pumps get to the end of their life they die completely, and no amount of hitting or anything else will persuade them otherwise. So, when an electronic pump falters way out in the boondocks, there's nothing for it but a long and expensive tow home. What price then an SU which a gentle tap prods into life?

(Written by Paul Walbran -

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