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MG MGB Technical - Fuel Pump question

Hi:

That's right! I do not have my friend's 1975 MGB running yet, and don't laugh either!

Last nite I was a breath away from firing it up, and couldn't get fuel to the carburetor.

I removed the fuel pump which was not working, and took the back "end cap" off, and found the contact points in bad shape. I may mess around with it today, but my questions are:

1) Has anyone installed an after market pump in the engine compartment, the kind we use to use way back in the 1960's on American V8's?

2) What is the pressure of the existing pump, that is, what kind of pressure does it place on the "float seat" in the carburetor?

As a side note, I an struggling with what was going on in the designers of these cars heads. For example why was the battery placed so far away from the starter, and in a location that is difficult to reach, that is subject to allowing leaking exhaust fumes into the passenger area, and that is exposed to road grime and road salt?

And why is fuel pump located in such hostile, and hard to reach place?

And why is the fuel pump more complex than it needs to be, with no apparent gain in reliability and life?

And---and---and!

Shut up Layne!!! Go fix the thing!!!!
Layne Wilson

Layne, you can mount it anywhere, TD's had it in the engine compartment. Max fuel pressure should be less than 4 psi normally around 2 psi is sufficiant. You can by a run of the mill electric fuel pump with higher pressure but you will have to install a fuel pressure regulator or you will flood the carbs. Only the engineers could tell you why they located parts where they did. As bad as part placement may be look at a modern car, they have taken it to a whole new level. Fuel pumps in the fuel tank, electronics buried everywhere, batteries buried under layers of parts, etc.
John H

Lane - For a list of various aftermarket fuel pumps and part numbers that are appropriate for the MGBs see my article on permanently installed back up fuel pumps at: http://www.custompistols.com/cars/dave/BackUpFuelPump.htm
The pumps for the 55 MG TF 1500 forward was located back by the tank instead of in the engine compartment to get away from fuel under vacuum (ie. being pulled from the tank to the pump) which tended to make vapor lock more of a problem. It does, however make changing the pump more of a problem. Just "messing" around with the points will most likely be an exercise in frustration for you. The pumps can be rebuilt, but is not always successful for the layman. The following link is a troubleshooting guide for fuel delivery problems and lists a number of people who repair/restore SU fuel pumps is you or you friend are so inclined: http://www.custompistols.com/cars/dave/ddFuelDeliveryTroubleshooting.htm
Cheers - Dave
David DuBois

Hi,

1) John, Thanks for the pressure info. I thought it would be in the 4 or less psi range.

2) David, I read the article on the extra pump, and it is a good idea.

3) At this juncture, my thinking is to either purchase the solid state replacement or an after market pump, such as a Carter, and if I go after market I will probably install in in the engine compartment.

4) What does "SU" mean, and also HIF? I see these initials used a lot. I am new to MG's and only have a Haynes manual.

5) As a side note, I played around with the pump today. It worked well out of the car, so I installed it and it didn't work. So I played around with the contacts. I could get it to start run for a while and then stop. With some coaxing it would run again---for maybe 30-45 seconds.Is their a set of points in the interior of the OEM pump, and if so would it be worth taking a look inside. I would like to get the car running tomorrow to see how the rebuilt engine runs.

6) I guess it is hard to beat the good old American V8, with the fuel pump arm cammed to the front of the cam shaft. Simple, highly reliable, good life, and easy to change on most engines.
Layne Wilson

Hi

Following is an added comment to the rediculous location of the battery in the 1975 MGB.

1) The starter can draw 80-100 amps, and represents by far the largest drain on the battery.

2) This fact means that the battery and starter should be as close as is physically in order to reduce the I sq R loss in the cable and to allow for a smaller diameter cable to be used.

3) Also the primary ground (common polarity, usually negative) of the battery should be terminated somewhere on the engine, and the body should receive its ground from the engine and/or the battery and in more than one place.

4) The negative battery ground on the MGB is inadequate. A 5/16 bolt through some 1/16 inch body metal is hardly a job well done. So the high starter current must find its way somehow from the engine to the body and back to the battery. This is hardly clear thinking engineering. And the next highest current drain, the head lights, must be feed through long lengths of larger wire because of the rediculous location of the battery. And all the many lower current wires, lights, etc, are switched from the dash, so, again wires are run forward to the switches and then back past the battery to the rear of the vehicle.

Layne

Layne Wilson
Layne Wilson

Layne. SU means Skinner's Union. HIF means Hoizontal Integral Float. The Skinner brothers formed the Skinner's Union and produced fuel system parts. One of their later designes incorporated the fuel chamber and the float (to shut off the fuel flow when the chamber was full) integral to the body of the carb. Earlier models, the "H" series and the "HS" series, used a seperate float bowl connected to the body of the carb.

As to the use of aftermarket pumps, my experience is that the current Fawcet brand pumps are not built to the quality they were some years ago. My daughter's car got over ten years our to a Fawcet pump. My Scout, and a friends, have not had two years before the Fawcet pumps shorted out. My current production SUs, and the original ones, have lasted much longer.

Yes, the SU fuel pumps, at least most of them, contain points and these can be changed out. Moss sells an SU carb manual, part number 211-345 at about $21 which will answer many of your questions.

I have, in the past, rebuilt my own fuel pumps. Recently, I sent a couple off to Dave DuBois to see how he did. As it turned out, he did quite well. I do not hesitate to recommend his services.

Les
Les Bengtson

Layne,I recently had a pump which worked out of the car but not in it.The problem was with the earth.Sounds simple but it wasn't!Suffice it to say I now have a seperate dedicated earth for the pump.
Peter Jones

Layne,
The "SU fuel pump", Its a sort of right of passage for all MG owners and the only bit on MGB’s that I don’t like. The design criteria went something along the lines of
Make it complicated,
Use lots and lots of excessively large bolts on it so it would not look out of place on Captain Nemos submarine,
Have as many small parts as you can and wherever possible use many small springs,
Where ever possible use gigantic pneumatic presses to assemble it so repairs are impossible.
And of course diligently search the entire underside of the car to find the most difficult to get at spot.
Make it so the pump protrudes obstructively into the luggage compartment, but in such a way that it isn’t easier to get at for repair, just so it gets in the way.
Make sure that there is plenty of mud and dirt as well because this is so good for the delicate springs and levers that make up the points.

Then design an incredibly laborious and Byzantine adjustment process required to get the thing to work.


After endless trouble (&time & $)with my SU (I also have a '75) one day I used the fuel pump from an '82 Subaru I happened to have. An emergency quick fix to get to work. I just stuffed it into that space in the back corner of the engine compartment. Took about 10 minutes to do and worked perfectly until I put in the Fuel injected V8, which needed a different sort of pump. It even made the same noises. Honda pumps work just as well.
Peter

HI,
1)Les, thanks for clearing up what "SU" means. I was seeing it often in my venture into MGB land.

Knowing the history of acronyms, and abbreviations is interesting and often useful. I sure wish these modern computer nerds who are writing computer books would wake up and put a definition-of-terms in the front, or back of their books.

2) Peter Jones, I have an electronic background and the ground to the pump was the first thing I checked, especially after I had scrutinizes how poorly the wiring scheme on the vehicle was. I also checked the positive 12V to the pump for excessive voltage drop under load. Your installing of a seperate ground using extra wire (something the manufacturer don't like to do) to reach a good grounding spot is correct thinking. I was considering doing the same thing after I resolve the pump problem. The puny pump ground is in a most hostile environment and invites trouble.

3) Peter Melbourne, it's 7:00 AM here, and I am on my first cup of coffee---your satire made me laugh.

4) To all, thanks for the help. Yes, somehow I will get this MGB running. A lady friends of the family bought it new. It has been sitting in a garage for 10 plus years with a "shot" engine. She knew I worked on cars as a hobby, and that I had rebuilt some engines over the years, so she bugged me for 4 years to fix the car. Being retired, finally I said yes. I have encountered some surprises, and expect to encounter some more. I told her the brakes are bad,including the master cylinder, once I get gas to the carburetor, I half expect carburetor trouble, etc.

5) It is nice to have a forum like this that can give "did that" knowledge, and experience.

Layne
Layne Wilson

Layne Layne Layne. There is absolutely nothing wrong with the MGB fuel pump and battery location. 500,000 MGBs can't be that wrong, especially when you consider how many are still running often as daily drivers 30 years and more after being manufactured. The fuel pump will last for years and years, and when it *does* start to fail usually gives you fair warning, responding to a thump to start working again. It is not the cars fault that owners tend to ignore warnings like that until they fail totally, at which point the owner usually blames the car, the people who built it, Abingdon, Uncle Tom Cobley and all, anyone but themselves.

The volt-drop in the battery cable is negligible, it is always connections which haven't been touched for years and years that cause the problems. With good connections you should be able to get the volt-drop between the battery posts and the starter down to just 2 or 3 tenths of a volt in each leg. I have seen 3v lost in bad connections just on one leg. I'll concede that *if* the battery were in the engine compartment and its ground post were connected directly to the engine there would be two less connections in the cranking circuit. But that method isn't universal on much more modern machinery where the battery *is* in the engine compartment.

I'll also concede that the pump, especially on chrome bumper cars, is in a very awkward place. But I was able to change it out on a car with all four wheels on the car and on the ground. Rubber bumper pumps having the electrical end in the boot *is* a great benefit. If the pump ground fails and isn't fixed then of course a new ground to elsewhere will get it working! But so would fixing the faulty manufacturers ground!
Paul Hunt 2

Paul,
I agree with everything you say about the MGB except with the grounding of the pump. I don't know enough about the wiring to say whether or not a previous owner had fiddled with it. I would not have earthed anything more critical than a boot light in the way it was done.

I did clean it up. I did get it working & I still didn't trust it. It was poorly positioned from the point of view of damage & vibration & frankly I'm surprised it lasted as long as it did in my ownership, without giving trouble.

I'm pretty sure that the earthing was i original - but I am certain that it was a poor piece of design & engineering.Sorry about the rant but it failed recently at a very inconvenient time and place!I feel so much better now.
Peter Jones

Layne, one note in defense of the battery placement.
Many years ago in my youth, I drove a tow truck for extra cash while in college. I cannot tell you how many battries I saw explode after a minor front end collision, frequently the hood would make contact between the post.... or just to the positive one and the resulting exposion and spreading of acid was very hazardous, and frequently did more damage to the motor compartment than the original collision. Hence...I have always found the battery placement in the "B" very comforting. Best of luck with your project.
Jim.
Jim K.

Layne, cheer up mate. The battery in my 95 Buick is located under the rear seat. If the car dies in the garage, I'm in deep severe as I could not get to it without pushing the car out into the driveway. the doors are so huge, the passenger side cannot be opened in the garage at all and the drivers side is a tight squeeze. Yes I am losing weight.

The fuel pump is located the fuel tank of both my 95 and 96 Buick. The 79 MGB pump failed and I just bought a solid state unit and the car runs fine.

Let us know how it turns out

cheers

Gary :>{D
79 mgb
gnhansen

Hi, I surrender!!

1) It was a perfect day here today. Shortly after lunch I went out to the garage to see if there is any thing I could do to get the pump running.

2) In short, I removed the blasted thing from the car again, and studied the point area in an effort to determine what might be wrong.

3) I found one of the rivetted contact points on the bottom assembly loose(The Haynes manual is in the garage, so don't know the correct name of the parts---I will wing it). I don't think the point (contact) was designed to flop around, and up and down approx 0.020.

4) Using a punch, I re-rivetted the point. I also found the points to be worn down so much that the lower assembly was hitting the plastic carriage, preventing the lower assembly from making proper contact with the upper points mounted on the forked spring.

5) Using a Dremel motor and a burr, I opened up the retangular hole in the plastic carriage. I also removed a bit of one side of the loweer brass point assembly.

6) Upon reassembly---dang---the thing worked. What a bummer!!!

7) I used it to pump the tank dry of 12 year old gas(probably 8-9 gal).

8) I now have clean (nearly anyway)gas at the carburetor, pumped their by an iffy pump. Yes, I am going to get some kind of new pump, but tomorrow I will attached the gas line hose to the carburetor and see if the carburetor is going to behave its self. I am not optimistlc. All I want from the pump is to last long enough to see if the engine, etc, is okay.

9) If the carburetor works, we may get to hear it run---a completely overhauled engine, including oversized pistons, etc.

10) I still don't have the PCV problem sorted out. I think I know what I want to do, but parts are thousands of miles away. I wish someone could tell me if the 3/8 diameter stub sticking out of the side of the carburetor toward the firewall is a metered (in essence a PCV valve) port. Just looking at it I am certain that it is on the atmosphere side if the the throttle plate.

11) If this port is metered why couldn't I attach the breather pipe to it, or better yet, the hose off the end of the tappet cover which is now going over to the charcoal canister, and attach the breather pipe to the atmospheric side of the air cleaner?

12) For those who may not have read, our lady friend listen to some mechanic shortly after purchasing the car in 1975, and he removed the air pump and its associated paraphernalia. He must have ben a nit-witt. He removed the fuel/air idle adjustment valve (course and fine) assembly from the side of the carburetor, and blocked off the two tiny ports in a half***** way. He left the fuel tank vapor line, the carburetor vent, and the tappet cover dead ended at the charcoal canister.

Layne
Layne Wilson

"I wish someone could tell me if the 3/8 diameter stub sticking out of the side of the carburetor toward the firewall is a metered (in essence a PCV valve) port."

I thought I had already told you that from your description that port *is* the PCV port. It *should* be on the atmosphere side of the throttle plate, because it is between there and the piston that the vacuum is controlled to a relatively constant low-level through the throttle range. It *should* have the breather pipe (coming from the front tappet chest cover) attached to it. Strictly speaking the port at the rear of the rocker cover should be sealed off and a vented oil filler cap fitted (which both filters and restricts) to put it back to non-emissions spec. However as I mentioned that might not be so obvious a mod, amnd someone might fit a 'correct for the year' non-vented oil filler cap which would stop the crankcase ventilation and cause condensation. It might be better to fit a small filter (e.g. K&N) to the port on the back of the rocker cover to make it more obvious. Piping something to the atmosphere side of the air cleaner is not really a good idea for two reasons - there is no point in putting uneccessary plumbing in when you are taking all the emissions plumbing out, it will add nothing, and especially to the atmosphere side which is unfiltered and allow dust to be sucked into the engine and possibly block the rocker cover port.

Other than one of clutter there is no good reason to remove the charcoal canister and its plumbing, it still helps the environment whilst detracting nothing from performance and economy, and has the negative effect of disabling the anti-runon valve if so equipped.
Paul Hunt 2

The ground for the fuel pump, while it would not have been my choice of grounding locations work fine if the surrounding surface has been properly prepared by sanding it down to a bright surface and then applying something like Kopr-Shield put out by Thomas & Betts to insure a good, corrsion free connection. That ground in our MGB has been working flawlesly for many years. Paul is absolutely right regarding the SU fuel pump, they will last as long as any other pump on the market and when they finally do wear out, all the parts are available to fix them properly. Too often though, owners try to cobble together a "fix" that works initially, but fails over time and then spend their time bad mouthing all things SU. Cheers - Dave
David DuBois

Hi,

1) Paul Hunt, if you read this, I moved the subject of PCV routing to the more applicable title "Rocker arm oiling, and PVC routing"

2) David, I cleaned up the pump ground and made sure it is integral. I agree with you that even though the fuel pump environment is hostile, a good ground can still be made there.

3) Also, where these MGB's are driven can vary widely, and, for example, running around Miami on black-top streets with no salt on the roads, is a lot different than, for example, Alberta, and a rural environment. This car's fuel pump was covered with caked up mud.

4) If I were to add another ground I would consider putting it inside of the trunk, attached to the screw holding the point assembly to the pump.

Layne Wilson
Layne Wilson

Layne,
The points in my pump failed, about 3 weeks ago, and I considered a new solid-state pump. The archives had some valuable information regarding the choice, and Moss also discouraged me from the SS unit, since there had been some problems (I appreciated this). The "point" is that, as Paul noted, if the points fail, they will probably still get you home, but the SS unit, once failed, remains failed. I found that out after I replaced the points, and there were problems (which I later resolved). Coming home from church one evening, the engine sputtered, and I knew immediately what the problem was. I and the wife pulled to the side and I accessed the points, since I had left the top cap off for access (I had been nervous about whether they would work reliably). I showed the wife how to put her finger on the points until it quit pumping, then jump back in the car. We made a mile, before the procedure was repeated, and we did this 6 times...but we made it home.

The problem was slop in the frame the top half of the points were mounted on, and the retaining clips would not hold the points steady. I removed the pump and threaded the plastic studs, so the points frame and outer cap are now "firmly" in place. It's worked reliably since then.

As a side note, the DPO had installed 1/4 inch fuel hosing. Not realizing the problem, I worked mightily for hours to get new fuel hoses installed, before I realized that it's a 5/16 inch system (I didn't know there were different sizes). Once the new hose was acquired, everything fits like a glove (not OJs glove...sorry, local humor).
Fred Doyen

The comments about a hostile environment for the pump ground puzzles me, the connection to the body should be in the boot/trunk under a number plate bolt, together with the tank sender ground and reversing lamp grounds, which *should* be pretty dry and clean. Whilst the connection at the pump itself is in a hostile place it doesn't seem to be that subject to problems, neither half being steel.
Paul Hunt 2

This thread was discussed between 29/09/2006 and 03/10/2006

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