Fuel Pump Pressure

[Malsprint]

I replaced the fuel pump on my Sprint with a Quinton Hazell replacement. The one I replaced had the shorter lever arm without the need for the spacer between the pump and the engine block. The new one has the longer arm and spacer. The new pump created a pressure of 10 psi. It caused the rear float bowl to overflow. I have read a few posts on here that talk about the higher pressure with some replacement pumps.

At first I thought the difference in pressure might be something to do with the longer lever arm creating more displacement in the pump. But it appears this is not the case.

There is a spring under the diaphragm inside the pump that determines the outlet pressure of the pump. The spring in the old pump was quite a bit shorter than the one in the new pump. I swapped them over and now the new pump is creating about 2 psi. This is an alternative solution to fitting a pressure regulator. I suppose you could also shorten the length of spring to obtain the same effect. If I had thought on I should have measured them both before fitting.

My question is since this is such an easy modification why does the replacement have a spring that is too long. The pump is listed as being suitable for a TR7 but a quick look on the TR site indicates that they also only need the low pressure. Is there another application for these pumps that need the higher pressure.

[cleverusername]

Parts for cars in general are rubbish and for classics the problem is even worse because of a relatively small market. Even paying more isn't a guarantee of getting better quality because allot of the time the parts come form one supplier or the quality could even vary from batch to batch. It is not unusual for things to be mis-calibrated, there are oil pumps with the wrong spring in as well.

To be fair the fuel pump issue doesn't bother me much because fitting a pressure regulator is a cheap and easy fix.

[dursley92]

I would have thought that as the pumps are intended for a selection of old British cars, that mostly all have SU carbs, they are being supplied wrong. All those SU equipped cars will need the lower 2-3psi pressure.
I like the weaker/shorter spring fix, very neat idea.

[cleverusername]

I would have thought that as the pumps are intended for a selection of old British cars, that mostly all have SU carbs, they are being supplied wrong. All those SU equipped cars will need the lower 2-3psi pressure.
I like the weaker/shorter spring fix, very neat idea.

Odds are they manufactured a batch of a few thousand before anyone realised they were wrongly calibrated. At which point it is cheaper to dump them on the market and let the buyer sort out the issues. I am afraid that is just how it is with car parts these days.