MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Fuel pressure regulator

I have had to fit a new fuel pump as the old one could not supply 2psi at full throttle for more than a couple of seconds. I have fitted a facet silver top. That pumps out 6 - 7 psi, so I need a fuel pressure regulator. I fitted a malpassi petrol king at the weekend and have a small problem, I can't stop the fuel leaking from the thing. I have tightened the unions as tight as I dare but there is still a leak. Should I be using any sealing medium around the threads? If so what? Or do I just keep on tightening until they stop leaking?
PS I have not cross threaded the unions or stripped the thread (yet!) and the flexible hoses are all new.

Thanks for your help.
D Brown

You have the wrong fuel pump. Use the lower pressure SS500 or 501, see here
http://www.fuelsystem.co.uk/web-facet.pdf
and the SUs are very happy with 4 psi without any other item of problem-inducing equipment !
David Smith

David,
The pump is fitted now so I will run with it for a while if I can stop the pressure regulator leaking. If that becomes a problem I will look at the ss500 or 501.
Thanks
D Brown

Regarding "if that becomes a problem",

...sounds like it already is a problem, fuel leaks are dangerous

If I were you, I would at least replace the faulty regulator for a good one that doesn't leak

or you can try thread sealant and try again with this one (the threads should typically be tightened 1, or 2 flats from "snug" on a compression fitting, and 1/4 ~ 3/4 turns on a pipe thread, if it is a pipe thread, then definitely with thread sealant (make sure it is fuel resistant first).

Probably your old SU just needed a new diaphragm, but each to his own.


Norm
Norm Kerr

I don't understand the comment about do threads need sealent?

Where are the threaded connections on the filter king, I thought they were push over type fittings

However all threaded connections I have found require sealant of some sort I personally use PTFE, I bet someone criticises that!
Bob Turbo Midget England

Norm SUs don't have diaphragms do they?
David Smith

Is your filter king of the type that is threaded with a taper thread for tapered thread fittings? If it is you are using tapered rather than straight fittings aren't you?

Photo?

Hi Bob, nuff said?
Daniel Thirteen-Twelve

"Norm SUs don't have diaphragms do they?"

Howdy, check out Item #36 in the below linked image:

http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=1420


Actually, an old fuel pump could have wear in any number of places, so I was being a little facetious when I said that before.

What was in my mind was, that is often easier to rebuild the one, worn part, than it is to replace it with parts that need additional parts in order to work right, especially if they, then, introduce problems of their own (regulators that don't hold a setting is one that I have heard others complain about in the past, or that leak is another, and that is what he's struggling with now).

What we need is for Facet to add a link to their website so that when an order is being processed, a question would pop up, "Is this for an A series engine? If so, please order our (part #) that pumps at the correct, lower pressure for that application and won't need a regulator."

Norm "nothing wrong with Facet pumps, but it seems like many people who buy them get the one that is too big and then need to add a regulator too" Kerr

Norm Kerr

of course Norm, sorry; mention SU and I think of carbs ! and some carbs have diaphragms too ;-)
David Smith

hello, I just took a look at the picture of the low pres pump and I see that there are two wires attached to it,---(one black,one red).Why is it advertised as a neg ground unit? Could one not just wire the red wire to the ground and the black on to the hot side? Often these pumps are soft mounted on rubber pads for quiet running,--in which case I would think there is no electrical connection to the case,(or is there?)Am I missing something here? Bob C in Kansas
chamberlain Bob

I've got the same setup on mine and I remember it leaking when I fitted it. I used PTFE on the threads but still had to tighten them up really tight. Get some PTFE on them and keep tightening till it stops leaking. Don't blame me if the taper fitting splits the ally casting though!! (that was my worry)
John Payne

I would think you should take the regulator back and get one that doesn't leak!
Tarquin

Yeah
Wrong pump and a regulator to strangle it back down to the proper pressure and probably strangle the flow rate as well - back to where you started
I'd be taking both back and getting the correct low pressure Hi flow pump But then I just like to keep things simple Willy
William Revit

Here is a picture of the regulator I have.
http://www.competitionsupplies.com/fuel-systems/fuel-pressure-regulators-&-gauges/petrol-king-fuel-pressure-regulator/67/8023
The brass looking unions screw in to the body.
I got a new pump because the SU replacement was not up to the job. On the rolling road I could hold full throttle for a few seconds before the fuel pressure dropped. Peter Baldwin (the rolling road and A series guru) recommended the pump and pressure regulator. Even the smaller pumps from Facet pump out 4.5 psi which could cause the SU float chambers to flood hence the need for a pressure regulator.
It looks like the leak is from the join between the brass union and the body of the regulator.
I keep tightening the unions thinking that I have tightened them enough, check for a leak, and then find that I can tighten them some more. They are now very tight with only a small leak but a leak all the same.
Is PTFE affected by petrol?

Dave
D Brown

I'd maybe try some form of joint/thread sealant, there are some petrol resistant ones around. The PTFE worked for me but I'd perhaps try something else next time. There is nothing wrong with the pump and reulator you are using but if you can't get it to seal I've been reliably informed these are a good alternative:

http://www.demon-tweeks.co.uk/Performance/Fuel_System/Fuel_Pressure_Regulators/Sytec_Pro_Flow_Fuel_Pressure_Regulator/809/2414

You just dial in the pressure you want, unlike the one you have where you really neede a gauge to set it up. Looks to have the same fittings though!
John Payne

Dave it would be worthwhile to do a root cause analysis of your problem - what spec is your engine?
David Smith

David,
It is very mildly tuned. +20 thou oversize, K & N filters with stub stacks, kent md256 cam, LCB and RC40 and maniflow inlet. Standard head.
The problem I have is that the fuel pressure regulator is leaking between the body and the brass unions. I only wanted to know how tight I should be screwing the unions into the body (as they are now very tight and must be close to stripping) and whether I should have used a thread sealant or not.
I am happy that the pump I bought is good enough, the old one was not and that I need a fuel pressure regulator to reduce the pressure before the carbs.
I have used a very similar setup in the past and it works well once set up.
I think I will be getting the PTFE out tonight.

Thanks fo rall your replies.

Dave.
D Brown

that is so near standard as makes no difference; several hundred thousand Spridgets have been running for 40 years with standard SU pump. If it were me I would have returned the 'recent' SU pump as faulty and requested replacement. Good luck with the PTFE, once that is sorted I trust you have a fuel pressure gauge to hand...
David Smith

Sounds like an opportunnity to convert to threaded fuel link fitings with AN adaptors instead of the brass. PTFE tape won't hurt.
Daniel Thirteen-Twelve

I have watched this thread with interest. One comment, made by the original poster, struck me: "I got a new pump because the SU replacement was not up to the job."

It would seem that there is an obvious fuel system problem because the original pump (a new replacement?) could not put out 2 psi of fuel pressure for any significant length of time. At that point, someone decided that the problem was the fuel pump rather than some other part of the fuel system. At that point, the decision was made to fit a high pressure pump and a fuel pressure regulator which will not seal properly.

What if the fuel system problem is not a bad fuel pump? All of the SU pumps I have used have been capable of providing proper pressure over the full range of throttle positions. I have not seen any mention of a pressure and volume check of the original fuel pump which would indicate it was properly tested and found lacking. (If this happened, it would indicate a bad pump and some form of replacement would be in order.) But, if this has not happened, you are treating a symptom by replacing parts without trouble shooting the system to find out the root cause of the problem. A partially blocked fuel line or a bad "sock" on the end of the fuel pick up tube would also cause a restriction in fuel flow that cannot be corrected by changing out a fuel pump.

Trouble shoot the system and find, if possible, exactly where the problem is, then correct it.

I agree with the people who feel the factory system, in good working order, is adequate for the needs of this engine specification. Since it is not proving adequate, the entire system needs to be checked out, one piece at a time, until the problem(s) is/are found.

Les
Les Bengtson

completely agree Les, that's what I've been trying to say all along - only not so eloquently !
David Smith

Les, David,
Thanks for your comments.
The problem arose when my car was on the rolling road. Peter Baldwin - the respected rolling road and A series guru over here, put a pressure gauge on the fuel line when the engine could not hold full power for more than a few seconds. The presure dropped and he said that he had found that was typical of the type of pump I had fitted (an electronic version of the normal SU) and it often could not cope with mildly tuned engines. He suggested fitting a better one, like the pacet silver top. I am sure there are other pumps that are also up to the job. This pump needs a presure regulator to stop the carbs flooding.
The reason for the thread was to find out if I should be using a thread sealer and how tight do I need to tighten the unions. I have tightened them very tight already. But every time I check that they are tight I find I can get another flat on them. At some point the threads are going to strip or the casing will break.
I realise that describing how tight something should be on a forum without giving a torque figure is very difficult but I was only expecting a general description and possibly some advice based on first hand experience of similar problems. Should they be finger tight, bloody tight, so tight you think the threads are going to strip, as tight as you dare plus another half turn, just keep going until the leak stops? Should I use some sealant if so what? Should I get it replaced?

Thanks in advance for your replies

Dave
D Brown

you ask for first hand experience; mine is that pressure regulators are a PITA and are best avoided, which they can be if the correct specification of pump is used.
David Smith

My experience with one of those pressure regulators is that I never had any problems with it.
David Billington

David, David,
Thn aks for your advice.
I have had a very similar setup 20 years ago on my first midget but with a smaller pump and a presure regulator with a filter underneath and had no problems what so ever with the set up. I know they work and deliver the goods. That was with an Oselli built 1400 fast road engine producing 105 BHP. That regulator/filter had the inlet/outlet unions fitted at the factory.
The one I have now has screw in unions that were not fitted at the factory.
The advice I asked for was regarding fitting the unions to the regulator.

Dave
D Brown

Hi,
Just thought I would give an update to the fuel leak. I removed the unions, cleaned any petrol off and refitted them with a little locktite thread lock and seal. Worked a treat. No more petrol dripping out.
The presure is adjusted to 3psi and there is no flooding from the floats.
The engine pulls better and is smoother throughout the rev ranges and in particular the higher end.
I am glad it is all sorted now.
And as ever, thanks for your help.
Dave.
D Brown

Glad you've got it sorted Dave.

Matt
Tarquin

Glad to hear that as my almost completely standard engine was on the rollers (I'd never been on the roller driving myself before, I wasn't very good at it - excuse getting used to new clutch)

I though Peter Baldwin didn't seem the type of guy to suggest fitting anything unnecessarily

Funny I thought about some lock thread whilst reading this thread (pun) before but didn't think it would be necessary on a new component or if it was someone would have experienced it before

Perhaps yours is out of a not quite 100% perfectly made batch (unless I've misunderstood what you put)
Nigel Atkins

After driving the car with the new pump, I think it was necessary. It drives so much better, smoother idle (even with a 123 dizzy), better drivability, revs better. It may all be in my mind but I would not go back to an SU.

I did the unions up so tight the I was starting to round the shoulders off (and that was with a quality spanner). I did them up at least two turns further that I first thought they should go and yet the threads were perfect when I dismantled them. I was quite suprised. Perhaps they weren't 100%
Dave
D Brown

This thread was discussed between 21/02/2011 and 01/03/2011

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.