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MG MGB Technical - Manual Fuel Pump - 77 MGB Roadster

Is the Manual fuel pump necessary? I just replaced my fuel filter and noticed some high pressure leaking from the Manual pump. I simply by-passed it and the car is running fine. In fact, it seems to have much better reaction to the accelerator. Of course, I could be way off by even calling this item the manual fuel pump. It's located just behind the carbs on the drivers side.
I just acquired this car and am in love with it.

Please copy any replies o my e-mail address, fleetcapt@aol.com

Bill Wiggins

Bill - I'm not sure what you are refering to when you say "manual" pump. Is this another pump in the fuel line besides the standard SU fuel pump? If so, why are you calling it a manual pump, is it someting you have to work by hand, or is there a switch that you have to throw to activate it? If the latter is the case, what you have is a permenantly installed backup pump, to be switched in in case the primary pump fails. If it is interfering with the standard pump, someone has used the wrong pump or the pump has a problem or it is not installed correctly. Let me know what you have and I may be able to help yousort it out. Cheers - Dave
David DuBois

Bill and Dave,
Some, maybe not all, ZS cars have this. It is described as a "fuel cut-off valve" in a picture in the Bentley book, but there is NO further information anywhere. It is after the filter in the line to the carb, mounted on the footbox next to the master cylinder. Has a pushbutton on it; I've never investigated its innards, I assume that under some condition it might shut off the gas. I always took it to be a sort of roll-over protection device, but recently realized that at least some of the cars with this also have the inertia switch under the dash, which kills the pump in a crash. Possibly a case of over reaction to US nonsense laws?
FRM
FR Millmore

This is called a Inertia Switch and for sure it is on the 1977 RB MGB and is located exactly where FRM has mentioned.

FRM is also correct as this is used when the car is hit or rolled over making the inertia switch shut off the fuel pump.

If this is what Bill is actually trying to relate to us than I would keep it. This is more for your safety than anything else.

Ray
http://www.treasure-island-jewelers.com/1977mgbSupercharged.htm
Ray 1977 MGB

Ray, I think he means something other than the inertia switch. If it is connected to the fuel line but isn't a pump or filter could it be one of those snake oil 'fuel enrichment' type devices someone has added in?

Simon Jansen

The cars in question have BOTH the inertia switch under the dash AND this "valve". All the cars around here that have it are 77s, but there are very few later cars in this area. I have seen some cars with the switch but no valve, don't recall the years of those. The switch is a switch, with wires; it turns off the power to the pump under high G loads or upside down. This valve has an "in" line, "out" line, and a pushbutton on the top, which you can depress with no effect. I assume that it functions like the inertia switch, only it mechanically blocks the fuel line under crash conditions. I've never seen one shut off, but then I've never had one upside down; consequently never had to reset one. It is definitely a factory piece.
FRM
FR Millmore

FRM is correct, it is a fuel cut-off valve and is found in tandem with the inertia cut-off switch located under the dash.

It has been my experience that these are VERY leak prone and the best solution is to bypass and/or remove it. Otherwise raw gas can pour onto the hot catalytic converter. I'm not positive, but believe that there was a factory recall on them and the dealerships disconnected them. Sometimes they were left in place, other times they were removed nothing but the mounting bracket was left behind.

Tom
Tom Sotomayor

Gentlemen,
Thank you for your input. After reading through these threads, it is most likely the roll over valve. I have bybassed it and the car is actually running better than before. I'm wondering if the leak may have been causing air to get into the line as well as drop the pressure to the carbs.

Trust me, I am NO mechanic. So your input has been great!

Regards
Bill
Bill

This thread was discussed between 13/09/2005 and 16/09/2005

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