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MG MGB Technical - Fuel Pump Surge?

Don't remember seeing a comment on this one before. I know my fuel pump has cratered and am getting ready to purchase a new one. The old one is the original SU on my 74B that would work sometimes and sometimes not. My question is-when this pump goes out, can it surge it's pressure up and down? ie too low to too high? Have had recent problems with fuel spitting out of the carb overflow. Thought it was sticking float, removed, cleaned, etc., ran fine for awhile and then quit. In other words should I go ahead and purchase the SU HIF rebuilt kit now or expect a fix with just the fuel pump?
Lowell Wakefield

Lowell - If you wil send me your e-mail address, I'll send you a write up of my SU fuel pump services. I may be able to save you some money by restoring and modifying your old pump to solid state. I have never seen a situation where the SU fuel pump will surge higher pressure. The maximum pressure in the SU is controlled by a spring that pushes the fuel (via the diaphragm) out of the pump. When the pressure reaches equalibrium with the spring, the pump just stops pumping. The pressure can go too low if the pump doesn't start pumping again the the correct pressure. I would suggest that you may want to rebuild your carburetors to eliminate the fuel coming out of the float chamber. Good luck - Dave
David DuBois

Just to tag myself onto this thread, what is the pressure normally found in the fuel line? I am thinking of putting a gauge of some sort in and would like to know the correct scale to get.

Cheers,
--
Olly S
Oliver Stephenson

Like David I cannot see how the SU can give a suddenly higher pressure given that the fuel is pushed along by a return spring and nothing else. Fuel overflow is usually caused by dirt in the fuel lodging on the valve seat. I'd replace the pump and see what happens before spending any more money. Normal fuel pressure in of the order of 2-3psi.
Paul Hunt

This thread was discussed between 28/05/2002 and 29/05/2002

MG MGB Technical index

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