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MG MGB Technical - fuel pump installation

New to the MG. I have a 76 MGB. I bought an electic fuel pump to replace the failed mechanical one I had but it came with no instructions. It would seem I have to run electrical connections where there were none before. Anyone do this conversion?
J DeCarlo

The MGB did not have a mechanical fuel pump. Your pump should be located in the trunk in the forward right corner connected to a white wire from the wiring harness. Make sure that the pump you are installing has an output pressure of 2 to 4 psi. If it is higher, which most aftermarket pumps are, you will need to install a pressure regulator. Otherwise you will drown the engine in gasoline.
John H

J. John is correct. The MGB always used an electric fuel pump made by Skinners Union (SU). There is a very good tech article on the SU fuel pump, along with one on fuel system troubleshooting, on my website, www.custompistols.com/ under the MG section. Both were written by David DuBois who both does an excellent job of rebuilding them and an excellent job of answering questions about them. His e-mail address is hot linked through the first article should he not appear here soon.

The location of the fuel pump varied over the years. From 77 onwards (my oldest RB car) they were partially in the trunk compartment, just as John mentions. They are at the right, front of the trunk and there should be a black cover, held on by two screws, over the upper end of the pump to prevent damage. The white wire goes to the portion of the pump in the trunk. The pump is isolated from the bulkhead by a rubber surround and held in place with a steel band type clip, vaguely similar to a hose clamp. The rear of the pump is forwards of the bulkhead and has the two connections for the fuel line from the tank and the fuel line to the carbs, along with the ground wire with attaches to a spade terminal near the base of the pump. The fuel lines are connected to banjo bolts and there are special, fiber, washers needed to keep the system from leaking when the banjo bolts are removed and replaced. They are not included in the new SU fuel pumps being sold and have to be ordered separately. I keep a few extras in stock as part of my spare parts inventory.

Older cars had the fuel pump mounted near the right battery box. Do not know which system was used with your car. If you do not see the pump protruding into the trunk area, put the rear axle up on jack stands, remove the right rear wheel and see what is actually there. A lot of changes may have been made over the last 29 years since your car was made.

Les
Les Bengtson

J. DeCarlo - If your MGB had a mechanical fuel pump installed, you either got a car that someone has swapped a B series engine from a non MG vehicle, or somebody replaced the original pump with a mechanical one in a misguided attempt to improve reliability. The original pump may well still be installed in the normal place and either disconnected and jumpered around, or the pump was removed and a jumper line was stuck in line. Check on the forward bulkhead of the trunk, slightly to the right of center and see if the original pump is still there. If it is (or even if it is gone, the wires for power and ground should be dangling in that position. If the original SU pump is still installed, it can be restored to proper operation (see my article on fuel delivery troubleshooting at: http://www.custompistols.com/cars/dave/ddFuelDeliveryTroubleshooting.htm
for a list of people who repair the pumps).

You don't say what kind of electric fuel pump you got as a relacement for the mechanical one, but it should be installed somewhere in the vacinity of the original pump. If the pump you got is a Facet pump, it will mount very nicely on the rear of the battery box (you need to make sure that the pump is the low pressure, 2.5 to 4 PSI before installing it). If you decide to have the original SU fuel pump (if it still exists) retored, I would suggest keeping the replacement pump and installing it as a backup - see my article on permanently installed back up pump at: http://www.custompistols.com/cars/dave/BackUpFuelPump.htm

If you have any questions, e-mail me at the above address. Cheers - Dave
David DuBois

Implicit in the advice from these guys - all more knowledgable than I am - is that caution should be used "improving" MGBs. Among the things I learned on this forum:

1) Tube shocks suck. They suck worse in the front (where they can be dangerous and break) than the rear (where they can make the ride worse).

2) Weber carbs - well, they suck, too. But then, as carburetors, they're supposed to. The downdraft variety that so many people use is neither as reliable, powerful, nor easy to set up as the original dual SU set up. The side draft Weber is useful - but on full performance set ups with the head, exhaust header, cam, rocker, followers, etc. all aligned to suck and blow much better than stock. The original Z-S that you may have is problematic, too, in that the water choke is unreliable and there's a plastic fuel line that came stock that's prone to cracking - right over the exhaust manifold. The downdraft Weber is better than the Z-S, but the dual SU is better (looks pretty good, too, and less like my wife's old Pinto).

3) The earlier cast iron stock exhaust manifold IS a header, and unless you've gone and done something extreme inside your motor (see carb comments), the only thing you save with an aftermarket header is weight, but they do tend to crack easily.

4) Electronic ignitions - don't exactly suck, but may fail (these are after-market pieces, after all) and then your stuck. Old-fashioned points and condensers can always be persuaded to get you home - some carry a spare P&C distributor for that belts & suspenders (or braces) reliability.

5) SU fuel pumps vs. aftermarket pumps. Like the electronic ignition situation, you can (usually) get an SU points operated fuel pump to get you home. The first failure mode is pitting on the points, and the classic rap with a hammer or the handle of a BF screwdriver temporarily restores function - and they can be repaired with the expense of under $10 for a new set of points. Not sure if you have that option on the "newer" pump on the '76, though. New solid block electronic pumps, though, may not be superior. Often the plastic casing is cheap and doesn't last long or can be damaged in installation (don't ask how I know). As counseled above, they may need a pressure regulator as well. And if they go bad, they go bad.

6) Most surprisingly, we typically yearn for the reliability of original Lucas parts. There are exceptions - alternators is one - but the curse of Lucas is most usually in the connections and grounds, which corrode over the years. Many a car's been parked for years after experiments with electrical systems have gone terribly awry.

7) This isn't to say modern stuff can't be good - there are good, valid and sometimes necessary upgrades out there. I made some jokes above - but just as there are well-engineered pieces out there, there are poorly designed "fixes", too. But despite what you may have heard, the people who put your car together the first time did know what they were doing.

Welcome to the world of MG! Don't be led astray by false myths and legends - these guys here on this BBS are the best! And most importantly, don't become a DPO!

John Z

Hello J,
Irresepective of what motor you've got, you need to run a wire off the ignition. In fact the orrigional wires to run the fuel pump should be in place still.
The electric fuel pump in MGB's is located (or was in your case) underneath the car and just infront of the RHS of the boot (trunk). Infact a part of it pokes through into the boot. If you look at the RHS back of the boot (back as in closest to the passenger compartment) you will see either a square metal cover, the round pump points cover, (if the square cover has been taken off), or a round hole, where the pump was.
There is a bundel of wires in that corner of the boot and a couple of them head down to where the pump should be. One is live when the ignition is on, the other is the earth, or negative. If you take off your rear right wheel you can see the location where the pump is or was.
In fact I grew very dissillusioned with the orrigional pump (kept stopping and would't be fixed) and bypassed it and instead put a SUBARU fuel pump from a 1982 wagon up in the engine compartment. On either side, at the back of the engine compartment is a neat little corner that could have been made to put petrol pumps. I pushed it in there with a bit of foam wrapped around it for sound insulation. The fuel lines and the location kept it very secure, and out of sight. You should use a filter. it worked very well until I put in the fuel injected V8, which needed a different sort of pump.
The wire that ran the orrigional fuel pump heads back from the fuse box near there. There is a bullet conection just back from the fuse box. On my car it is a white wire and it is just a matter of unplugging the rearward bound wire and plugging in your new connection.
Peter

Seeing the quality and thoughtfulness of the answers here makes me proud be associated with the MG marque. "The marque of friendship", indeed. "You guys" are great.

Phil
Phil Jones

There was indeed wires still present in front of the boot (under the car). One wire went to a switch under the dashboard marked 'fuel pump' (a good sign). I'll check the voltage output of the wire to be sure it's 12 V to ground. This was actually connected to the old fuel pump but there was no ground wire. That's what confused me. I can only guess it was the case to ground.
Interestingly, another taped up wire (dangling listlessly unused) was located in the same vicinity but appeared to go to the ignition coil(?). Old connection?

Anyway again for all the help and great suggestions. Should have it going (I hope) in a few days.

J.

Jerry DeCarlo

I assume the wire you think goes to the coil is a white wire, if so it is the original power input to the fuel pump. Don't know what you may find on the wire going to the switch on the dash. After-market and original fuel pumps I have seen had a ground wire.

Clifton
Clifton Gordon

If the dangling wire went *direct* to the coil then it is a PO wire and for that and the other wire going to a switch you are on your own. It could have been for any reason, possibly the original in the rear harness damaged, or the bullet connectors faulty and they decided on a bypass rather than a fix. As Clifton says all factory wiring included a ground for the pump, which went back to a rear number plate bolt. There should also be one vent pipe from the body of the pump going into the boot or a nipple on the chassis rail (two vents going to T-pieces in the boot on chrome bumper cars).
Paul Hunt 2

This thread was discussed between 17/04/2007 and 24/04/2007

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