Fuel pump problem!

[Phidi]

I’m still having problems getting my mk11 running reliably. I’ve had a lot of help here already, for which many thanks.
Situation now is my original pump (Hardi) started to pump like a machine gun before slowing to a smoother regular stroke - still about 1 stroke a second . Decided to replace it with the same type (unfortunately on disconnecting the fuel line, the pipe was seized in the union and split. New fuel pipe in copper fitted but on tightening the tank end, the union nut sheared off so now it was also a tank out job - at least it was a chance to flush out the tank.) with another new fuel pipe fitted, the new pump was fitted and worked perfectly for about ten minutes at tickover before suddenly throwing in a dozen or so rapid strokes. On turning the ignition on, the pump does the normal couple of strokes before actually starting, goes into a regular one second or so stroke before sounding like a machine gun for a few seconds
and then repeats. Is this actually normal? Or does anyone have an idea of what might be wrong? Thanks in advance.

[simmitc]

Is it the correct pump? With SU pumps there are some mounted under the bonnet, like the Minor, that suck and others, like the mini, mounted by the tank that push petrol to the carb. I do not know whether Hardi are the same.

[les]

What is this fascination with Hardi pumps ?

[svenedin]

Is it the correct pump? With SU pumps there are some mounted under the bonnet, like the Minor, that suck and others, like the mini, mounted by the tank that push petrol to the carb. I do not know whether Hardi are the same.

Arguably any Hardi pump is not the right pump. The right pump is SU AUA66. Hardi pumps produce higher pressure than the SU LP (low pressure pumps). This can produce problems with the sealing of the float needle valve and flooding of the float chamber.


Incidentally, although fuel pipes are available in copper I would only ever use a Kunifer fuel pipe as these will not work harden from vibration and fracture. Same with brake pipes.

Stephen

[svenedin]

What is this fascination with Hardi pumps ?

They're cheaper than SU pumps..........

Stephen

[les]

———— probably not in the long run ! We all need to watch the cash but buying cheap only encourages suppliers to cut down on genuine stuff ! That’s why we get iffy parts.

[geoberni]

Is it the correct pump? With SU pumps there are some mounted under the bonnet, like the Minor, that suck and others, like the mini, mounted by the tank that push petrol to the carb. I do not know whether Hardi are the same.

Hardi do offer a variety of part numbers, serving under bonnet and under car applications:

https://www.hardi-automotive.com/wp-con ... rzeuge.pdf

1112-5 is supposedly only for the Minor.

But as I posted last year, while this is the lowest pressure pump they make, it's nearly double that of the SU Pump intended for the SU Carburettor.
viewtopic.php?p=696587#p696587

It sounds to me that the OP has a leak somewhere, either air being sucked in, or fuel being pumped out....

[svenedin]

———— probably not in the long run ! We all need to watch the cash but buying cheap only encourages suppliers to cut down on genuine stuff ! That’s why we get iffy parts.

I think that's right. The Hardi pumps are not user serviceable whereas the SU pumps can be rebuilt and almost every single part is available.

Stephen

[mike1864]

And the Hardi has no integral filter. So crud has an increased chance of getting to the pump's diaphragm or to the carb.

[Phidi]

Thanks for all the pointers, I shall give this pump (it is an under bonnet sucker type) a run to see if it will last for a while and in the meantime save up for a genuine SU pump. I appreciate the comment on using copper pipe but to try and avoid work hardening I have lined the securing points with rubber type inserts and put in several bends to take up any thermal movement - but I do agree C/N is the better option.

[svenedin]

Thanks for all the pointers, I shall give this pump (it is an under bonnet sucker type) a run to see if it will last for a while and in the meantime save up for a genuine SU pump. I appreciate the comment on using copper pipe but to try and avoid work hardening I have lined the securing points with rubber type inserts and put in several bends to take up any thermal movement - but I do agree C/N is the better option.

I only mention it because suppliers such as ESM offer that fuel pipe in either copper or Kunifer.

Stephen

[svenedin]

Good Luck!

As Berni has said, with a diaphragm type pump (whether SU or Hardi) if it will not stop ticking it is either leaking on the inlet side (drawing in air) or leaking on the outlet side (overfilling the float chamber or leaking from a hole in the flexible hose or at a joint). The Hardi pump is much more likely to flood the float chamber because it operates at a higher pressure than the SU so if the float needle is only sealing marginally (due to wear) it can carry on pumping.

I am not familiar with the internals of a Hardi pump but I assume it is broadly similar to an SU. There is a non-return valve on the SU to prevent fuel flowing backwards at the inlet. This can become ineffective due to rust or dirt in the fuel.

Stephen

[Mervin]

"What is this fascination with Hardi pumps ?"

They've been Made in Germany since 1938. I wonder if they are now? It will be the fallacy of "superior" German engineering.