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MG MGB Technical - Auxillary Fuel Pump

I have mounted and plumbed a small after market Facet fuel pump up in the engine bay. I atteched it to the fender just before where the fuel line goes around to connect to the carbs. (72 MGB-GT). Can anyone advise me on where is the best location from which to get the 12v power I need to operate it. I would like to have a switch located in the cockpit so I can power it on if the main fuel pump should go out while on the road.
Thanks,
John Fraioli
John F.

If you are having a switch in the cockpit then that needs to pick up the 12v supply and feed it to the pump, in which case it should be a green (fused ignition) wire of which there are many in that area like for the tach, voltage stabiliser, etc. Alternatively the switch could put out a ground, and the pump needs to be backed by a fused ignition supply i.e. from the fusebox green.

But will a Facet pull fuel all that way and through the standard pump? And will it deliver too much pressure for the carbs? Many after-market pumps need a pressure regulator.

I know various people fit these, but really it is a once in 20 year thing in my experience. And it also needs to be used regularly, for short periods at any rate, so it *will* work as a standby if the main fails. For this you need a changeover switch to turn one pump off and the other on. This can be inserted where the rear harness joins the main harness near the fusebox. But the standard pump feed is unfused ignition (white) and I would strongly recommend fitting an in-line fuse here, irrespective of whether a standby pump is being installed or not.
Paul Hunt 2

John - Make sure that your Facet pump is one of the low pressure models (2.5 - 4psi) and it will be fine. Both it an the original SU pumps have just check valves in the flow path, so either will pump through the other. I routed the power lead for the original pump to a single pole, double throw switch mounted on the vertical bulkhead behind the passenger seat to switch power from one pump to the other. See my article on permanently installed back up fuel pumps at: http://homepages.donobi.net/sufuelpumps/Fuel%20Pumps/Back%20up%20Fuel%20Pump.pdf
Cheers - Dave
David DuBois

Ok, it looks like that link doesn't work so just go to my web page at: http://homepages.donobi.net/sufuelpumps/ click on Fuel pump articles and then on Back up fuel pump. Cheers - Dave
David DuBois

I highly recommend David's installation.
rick ingram

Thanks Paul, Dave & Rick.
I like the idea of the three position switch. Run one pump or the other or neither. I am using a Purolator "POSI-FLO" pump rated 1.5-4.0 PSI. Here is a picture of where I have mounted it. I have not connected power to it yet. But so far the original SU pump is able to pump through it just fine with plenty of volume. I'll let you know how it works once I wire in the switch.
John Fraioli
1979 Inca Yellow MBG
1972 Teal Blue MGB-GT

John Fraioli

Forgive my misuse of this space, but I need to see if the fix we put in my web site is going to work on this BBS
http://homepages.donobi.net/sufuelpumps/othertecharticles.html

http://homepages.donobi.net/sufuelpumps/Other_Subjects/Electrical/General/Brake_Light_Relay.pdf

http://homepages.donobi.net/sufuelpumps/Other%20Subjects/Electrical/General/Ground%20Point%20Preparation.pdf
David DuBois

David, the last link didn't work. Others fine. Thanks.
Robert McCoy

The last link doesn't work becasue it has '%20' embedded in the URL instead of the required '_'. If you substitute the underline it does work.
Paul Hunt 2

Robert and Paul - Thanks for the feedback on the links. My wife just finished putting a web site together for me and since she is a novice at it, we noticed that the links failed on some sites.

Paul - Our son in law also told us about the %20 being an archaic notation and Liz removed them in favor of the '_' which has fixed the problem. I could have saved myself a phone call if I had just e-mailed you.

To all - thank you for your patience with my experimenting on this BBS to insure that the web site works properly. Cheers - Dave

David DuBois

No...thank you, David, for your helpful tech hints!
rick ingram

Happy to help, Dave. If you had just asked me why the one didn't work without me seeing the others I probably wouldn't have spotted it anyway. It was only when I saw the underlines on the other two that I remembered that HTML codes for special characters do cause problems in links, spaces is another one. I tend to avoid anything other than alphanumerics as a result, and even mixed can cause a problem on some servers!
Paul Hunt 2

This thread was discussed between 23/02/2008 and 27/02/2008

MG MGB Technical index

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