Malpassi fuel pressure regulator question
Turbo Mini Forums

Hi all, I had a quick look through the search function but couldn't find a definitive answer for this.
Is it possible to use a malpassi fuel pressure regulator as a way of sending fuel back to the tank to stop fuel pressure at the carb being too high!
It may sound strange (or stupid) question but I have a spare regulator the car is N/A and I was advised by min-its to use a facet red top fuel pump (this seems to be putting too much pressure through even having the current combined Malpassi fuel filter and regulator turned very low).

Could someone possibly let me know what the four connections on the fuel pressure regulator from the metro turbo cars are, I would of thought there would be fuel in, fuel out and a return maybe opposite the adjustment screw to send excess fuel back to the tank? So what is the fourth one for?

What I thought I could do was turn my current combined regulator and filter up and when there is too much fuel pressure for the carb it will return to the tank but when it is needed as higher rev's then the pressure should be correct.

Would this work? If I get hold of a fuel pressure gauge would kind of pressure should I be needing on a 1380 with a 286 cam and an HS4 SU carburettor?

I know I could just use an SU fuel pump but I thought since I have now paid out for the red top I might as well use it!

Many Thanks Matt.

Hi,
Just set it at 3.5 psi ish and you should be sorted...
Cheers,
Gavin :)

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Yes, that's exactly what such a FPR is for !!!!

Although in the instance of a turbo, there is a port to raise or lower fuel pressure relative to intake pressure.

Uppermost is a boost/vac source. ( intake manifold )

Next 2 lower ones are fuel inlet and outlet to carb.
One pointing down is the return to the fuel tank.

I thought most of them were labelled with an arrow anyway ?

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When you say it is putting too much pressure through what are the symptons. You should not need a regulator with the fuel pump you are using.

I assume that you have an SU carb, have you replaced the float bowl needle valve recently?

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Yes it is an SU carb, an HS4.

The reason I have said it is putting to much pressure through is I have been told (maybe rightly or wrongly) that once the fuel is pumping it should get to the correct pressure and the pump should switch off until it is needed again.

I take it the facet red top does not do this as I can always here it pump and surely you do not want it constantly pumping if the car is just idling because could it not burst the seals in the carburetter?

Or would it be fine if set at 3.5psi whether it is idling or at full rev's?


Thanks Matt

would i be right in saying that at idle the Pressure will be 3.5psi but the FLOW will be low as it is not being used. but then at full chat you would still have 3.5psi pressure but a HIGH FLOW to cope with the needs?

I and many other people have run this setup with no problem. The pump is quite happy pumping against the float bowl valve. Do you think that a mechanical pump on the cam stops when the float bowl is full?

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Someone is getting confused messages I think.

Some older type electric pumps did stall when 3.5psi (ish) was reached, but the one you have will just keep ticking.

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we use the red top pumps on the miglia's they do stop ticking when the fuel pressure is high enough

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So would that suggest my fuel pressure is not high enough then, it drives very well (as far as I am aware).

The regulator is currently turned down very low, approx how many revolutions of the nuts should it take to reach 3.5 psi?

Thanks guys

get a Feul pressure Gauge mate. The only way to do it properly.