Which Malpassi fuel pressure regulator for MK2 3.8?

Hi folks, just joined up.

I’ve got a '62 MK2, and I’ve decided to fit the Malpassi pressure regulator w/filter - the car’s been spewing gas out the float vent tubes, and fitting a new SU replacement pump (the car came with a generic pump rated 4.5 to 9 lbs.) hasn’t addressed the issue.

On their site, there’s a number of models/part numbers, but no way to know which one is best suited to fit my car…also, since there’s no gauge on the unit, I’m curious how one knows what the output pressure is.fitted one, and if so can you supply me with this info?

Actually, if there’s any other supplier of a unit that meets this criteria, I’m all ears!

Thanks!

There should be no need for a pressure regulator, never heard anyone using one.
I think your SU needs a rebuild ( with new fuel valves that have nylon tips )

3 Likes

Hi,

I think the new needle valves for the float chambers are Viton tipped. If it is related to nylon is beyond my chemical knowledge.

But I agree that no fuel pressure regulator is necessary, maybe your floats are no good, or the float chamber setup and needle valves are incorrectly installed?

Cheers!

Thanks for chiming in Peter, but I think maybe you didn’t understand my post…the pump is brand-new, sold to me as OEM fitment for my car.

I asked this because there’s a number of posts on this site that specifically address this issue.

Hi Pekka,

Fwiw, the carbs are properly sorted with all the correct components, and two different types of “use only these” float needle/seat assemblies have been tried, with two different float heights tried as well…we’re down to the two most common causes of fuel being blown out the overflow pipes - faulty, dirty or mis-adjusted float needle(s), or excessive fuel pressure.

Firstly, I agree that a regulator should not be needed.

However, I had exactly this same problem, albeit on an XJ6 fitted with HS8 carbs.

When I fitted two new fuel pumps, the overflowing started.

The needle valves were brand new with Viton tips. I checked both floats, which proved to be fine. I fitted a new filter and cleaned the tips in case there was any dirt on the seat.

The issue would come and go. First one carb and then the other.

In the end, I checked the fuel pressure being delivered by the pumps, and it came up at 5.5 p.s.i. Checking around, it seemed to be that the ideal pressure should be 3.5 p.s.i.

I fitted a Malpassi regulator and set the pressure to 3.5 p.s.i. and the overflowing stopped.

This is the regulator I fitted -

If I were you, I would check the fuel pressure first and if that is correct you can be sure that the problem lies with either the needle valves or floats.

I never had any trouble with overflowing with the original pumps.

So much for modern replacement parts.

Dave

Did you check the float itself, common issue is sinking floats.
They sell now a type of float that can never sink again.
I know nobody ever using a pressure regulator.

2 Likes

Chris,

Depending on the model, an SU HP pump will provide 2.7 to 3.5 psi fuel pressure which is suitable for HD6 and HD8 carbs, with no pressure regulator required or normally provided. Volume is 15 gph which is about 1 quart per minute. Which SU pump have you installed?

An alternate pump providing 4.5 to 9 psi would need a regulator but that should no longer be necessary, and fuel leaks from vent tubes are more likely valve or float related as suggested above.

1 Like

Hey thanks Dave, just the info I needed. :+1:

Second thing I checked, right after the needles and seats…they’re the brass ones, dry as a bone inside too. :grinning:

Fuel pumps should be 1.5 to 3 psi for our cars. Since you already have this pump goes with the regulator unless you can make a return to the vendor for an exchange. My monster 6.6 liter 400 CI GTO only takes 5psi or you flood the needles and everything goes wonky!. Keep us informed

I have this filter regulator on my cars as the new SU pumps I bought were all in excess of 3.5 psi. First thing you should do is measure the pump output. Please also confirm you have the correct washers in the correct sequence on the float bowls.

Isn’t the pressure of the SU pump determined by the tension on the armature coil spring under the diaphragm. Different springs for different pumps or miscalibrated springs causing excess pressures??

My problem only started when I fitted the new fuel pumps.

As I said, this was on an XJ6 with HS8 carbs. The fuel pumps are the submersible AC Delco type, so not SU. The output pressure is not adjustable.

The needle vales worked perfectly with the original pumps.

When I did test the output pressure, it was too high, so that was causing the overflowing.

My feelings are that the modern replacement parts are pretty poor quality. Not only was the pressure too high, but they are much noisier than the originals.
I’ve had difficulties with numerous replacement parts over the years, and it seems that it’s not getting any better.

Dave

So I’ll be back in Ca. to the car in a week (waiting for these new rainstorms to pass), and I have both a new pressure gauge and Malpassi regulator waiting for me.

Thanks Dave, as well everyone else who’s chimed in…I’ll report back soon with the results!

I am wondering how you got on with this.

Did you get the regulator fitted, and if so, did it fix your issues?

Dave