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 MGB Technical - Fuel pump - positive or negative ground?

As you may have read in an earlier posting (the one where the rear leaf spring has been hitting against the supply line), my '67 B has fuel system issues. Rather than trust the old pump (it has let me down & a freindly knock on it resurrected it) and attempt re-do points/diapghram/etc...I've decided to replace it with another SU...yeah, I know what some of you are saying, but I'm old-school & prefer originality where possible.

My suppliers asked if I need a positive or negative ground pump, & rather than having him tell me what I need, I'd rather run it past some expert eyes/ears on this board.

Originally, my car was positive ground. A few years ago, I had it converted to negative ground. To do this, polarity was changed, but the generator/regulator are still in situ. The only mechanical changes were the battery terminals and the tachometer. The fuel pump was never changed as I never thought about it at the time.

Obviously, it's a positive ground pump...or is it obvious? Does it matter whether I order the positive or negative? My guess is that I need a negative ground pump, right?

Some of you may be thinking that my fuel system problems may be related to the positive-to-negative ground change, but that was several years and over 5k miles ago.

Any thoughts?
Gary NJ

Your car is set up for negative ground, thus you need a negative ground pump. I seem to recall that the early pumps were polarity-insensitive, but I could be mistaken....
Rob Edwards

Rob is dead on. The new pumps are electronic and the old ones were not. As such the old were insensitive to polarity. The electronic ones are. Order a negative ground replacement.
Paul Hanley

Thanks! I was leaning towards the negative ground, but I'm glad it has been confirmed. I'll be ordering new flex hoses, too.

Now, are there any tips/tricks on how to ensure "leak-free" connections @ the banjo bolts? I've never removed or installed these before & anything that I can find out beforehand is certainly appreciated.

Are there any other pieces that I would need in performing this operation?

thanks again to all who offer excellent advice on this board!!!
Gary NJ

Leak Prevention: Use new copper washers at the banjos, and of course, make sure everything's clean when you bolt it up.
Matt Kulka


Gary,

Seem to remember that some pumps had a diode. Changing polarity works OK but burn out of the points occurs. This takes a while but I have no idea how long.

John
John U

Even the later MGB pumps with points were polarity sensitive, not just the much more recent pointless ones, as they had a diode quench instead of a capacitor. You can connect a diode pump quench the wrong way round and nothing drastic will immediately happen, but the quenching effect will be reduced. But don't connect a pointless pump the wrong way round. And if you'll take my advice you'll avoid a pointless pump. They don't respond to a gentle thump so you are stuffed until they either decide to work again, which was what mine started doing, or you get a tow home. I junked mine and went back to a points-type.
Paul Hunt

This thread was discussed on 12/05/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.