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MG MGA - Fuel pump pressure

I recall some threads a while back on excessive fuel pump pressure causing leaky float valves and overflowing carb bridge fuel level. Can someone remind me what the outcome was re an appropriate fuel pressure. I have an MGB electronic SU fuel pump which may be high at a stated 3.7psi? I recall (Steve or Colin?) adding a pressure regulator with good outcome. Is that the way to go?
Mine is a Twin Cam engine but I doubt that has much of a difference in fuel pressure and flow requirements.
Any thoughts gratefully received.
Best
Bruce.
Bruce Mayo

Hi Bruce
( a different Colyn here :^)

to the best of my knowledge, the best pressure for SU carbs is in the region of 1.5 to 3.5 psi, so your 3.7 psi is a little on the high side.

I have a Facet aftermarket fuel pump on my MGA and it did cause over fuelling problems on the H4 carbs that I used to run with. It was delivering over 5 psi which used to overwhelm the float valve.

So I installed a Filter King which combined a fuel-regulator and a fuel-filter and I set the fuel pressure at just under 2 psi and this solved the problem.

The Filter King has a useful option of a take off point into which you can temporarily install a fuel pressure gauge. this made it really easy to set the fuel pressure.

I have since swapped my 1840cc engine for a 1950 cc unit which has a Weber 45 DCOE, the Weber runs better with 3.5 to 4 psi and I easily reset the fuel pressure with the Filter King to suit.

I have attached a picture of the Filter King unit installed on the front of the heater shelf.

Cheers
Colyn

PS. The extra f in front of the caption is a typo and not me stuttering :^)





Colyn Firth

I had to take a second glance at Colyn's post. First read through I thought he was quoting text of my experience.

Until dropping the pressure to under 2psi I had been unable to weaken the fuel fully. It certainly helped and I got about 50% improvement in the weakening process. It was only about a year later or so I discovered both jets were worn oval and this was with relatively recent reconditioned carbs. I subsequently found out they had not been replaced during the overhaul. All is now good.

Steve

Steve Gyles

Bruce
A std. mga twin cam fuel pump is a high volume/ low pressure pump and it's output is rated at 48ins which is 1.73 lb
If you're going to regulate your MGB pump down you will need to check fuel flow at your new regulated pressure--A std T/C MGA pump is rated at 54litres/hour which is less than a litre/min and borderline for spirited driving
Even the factory had 2 pumps on their racers
I'd respectfully suggest that you measure your output after adjusting your regulator and make sure you're getting at least a litre per min---minimum, preferably more
An MGB pump should do this easily BUT it depends on the makeup of which regulator you go for as to if the output is restricted by dropping the pressure
It will pay to check, you know what happens to T/C pistons-------------

willy
William Revit

Great feedback you guys and thanks.
Willy. Being a slow convert, and even now sitting somewhere between Imperial and Metric most of the time (!), can I take it that 1.73lbs which you quote means 1.73psi?
Best
Bruce.
Bruce Mayo

Yep, sorry, 1.73 pounds per square inch, not much is it--?
Honestly I don't think you will need to screw your MGB pump down quite that low to stop the flooding, but if you do it will pay to check the flow after the regulator to make sure you're still getting enough---
Cheers
willy
William Revit

Hopefully no one will mind me keeping this thread alive (until I can report a successful conclusion) by reporting progress to-date. In anticipation of proving an over-pressure pump on my car I have purchased a Malpassi Italian Petrol King pressure regulator and am about to check the actual pump pressure and rate of flow against the pump’s spec sheet without it first of all. That should prove it’s needed, but a bit embarrassing if not! Then the plan is to fit the regulator and adjust it to around 1.7/2.0 psi as suggested by Willy, and ensure the flow is still minimum 1 litre/min.
By Sod’s Law, immediately after buying the Petrol King my brother found and donated a Sytec fuel pressure regulator which had been lying unused in his garage for many years. So, which of these two units should I use? Any suggestions which one is “best”? Certainly the Malpassi units have been around for years and are well known.
Also, I propose to fit whichever unit in line close to the output of the pump to keep it out of sight for originality. Ok?
Bruce.
Bruce Mayo

Bruce,
I meant to add that when I fitted a Filter King Fuel Regulator, which is basically the same as your Filter King except that it has a built in fuel filter, I was careful to make sure that it had the same internal diameter inlet and exit pipes as my existing fuel pipe (mine is now has an 8mm internal diameter).
This was to prevent placing a flow restriction into the fuel line.

I had replaced my entire fuel line because the old one was a flexible rubber type and it was deteriorating and developing leaks.

Cheers
Colyn
Colyn Firth

Bruce
I'd test both and go for the one that gives the best flow
Colyn makes a good point about fuel fittings, it always pays to check the bore size and drill them out if needed
I've lost count of how many of them universal plastic filters I've pulled off cars with 5/16" fuel lines that still had the 1/4" ends on the filters with the piddly little holes
cheers
willy
William Revit

More for other viewers to here, it's beyond me why some insist on paying through the nose for an SU logo on the label, and then to have all this fuss, you shouldn't need a regulator.

I went Hardi (type) fuel pump very soon after getting my midget 13 years ago and it has been fit 'n' forget as it should be with a petrol pump.

You don't even have to have the usual one the suppliers say and can chose different fittings to pump head if you want.

The Hardi pump adjusts itself to what the carbs need, from idle to WOT.

You're suppose to have a filter before the pump but I've never had one but I have added and used (smaller) disposable plastic types just before the carbs, although the Spridgets never had these as standard so now my stock of them has run out I might just run a length of fuel hose as my tank is only a few years old.






Nigel Atkins

I bought my A 32 years ago with a Hardi pump in it. I had my first problem with it a month ago when I started the car for the first time in 8 years. There was a very slight leak. I took it off, cleaned it up, reinstalled and haven't looked at it since.

There are very few parts on the car I can say that about.
DJ Zurawski

Thanks everyone for comments.
Nigel, fwiw, I decided to replace the SU pump on my car which at that time was very aged and in need of further attention to the contact points, a fairly frequent occurence. Whilst not a cheap solution admittedly, decided to take the bull by the horns and change to an “electronic” (no points) version of SU as it simply replaced the old pump and bolted straight in to the box by the rear axle and utilised the existing piping and unions. An easy fix. Have never regretted the outlay, it having functioned faultlessly now for 15 years, so justifying my “paying through the nose for an SU logo on the label”!
Bruce.
Bruce Mayo

Bruce,
your car and your money so obviously you do as you prefer, I wasn't trying to convert the SU faithful.

I'd always pay more for better quality, reliability and longevity but just as an example Moss sell a MGB SU electronic at £135 where as the Hardi is £88.50 and as the Hardi are so good I'd call that paying through the nose for the SU logo on the label.

I'm at a loss why you should need a regulator with the SU but you wouldn't with the Hardi reducing the additional component and removing even more price differential.

I'm glad to hear the SU electronic pump has provided such good service as I've seen complaints about the SU electronic but I can't remember if it was conversion kits or newer pumps or both and IIRC the price of service/conversion kit got you a good way to the cost of a brand new Hardi pump.

As I put in my post it was more for other viewers, to show a very good quality alternative, and at a much lower purchase cost.
Nigel Atkins

This thread was discussed between 16/04/2021 and 23/04/2021

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