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MG MGB Technical - Fuel Pump Won't Quit

My fuel pump, an electronic SU, is driving me crazy. I switched pumps last year when I changed from positive to negative ground (car is a stock '64B). Now, the pump does not stop ticking, despite the float valves being closed. There is no fuel coming out the overflows, and when I pumped fuel into a container there were no air bubbles. The fuel tank is full, and I just removed the input/output valve cage and cleaned it, as well as the filter. I have no other filter in the system, and the line from the tank is a hard line. So, anyone have a suggestion for what else to check as I am at my wits end.

Don
don scott

Don - Did you check the valve reeds themselves? They could have some debris under the one of the valves or one of them could have a split reed. I suppose that it is possible that the diaphragm is short cycling. While I have never seen that sort of thing, nothing is impossible. Cheers - Dave
David DuBois

If there is no leak from the fuel system pressure must be leaking back from the pump chamber into the inlet port, i.e. the non-return valve Dave mentions is faulty.
PaulH Solihull

Further update - so I re-checked the valves and connections, even disassembled my positive ground pump for comparison. The valve disks were in good shape, no debris in the pump, no leaking anywhere, the screws around the pump body were a little loose so I tightened them up. Put everything back together and the pump still ran on - no change in the speed of the pumping action, although the sound changed a little bit (became a little more muffled). So I proceeded with the rebalancing my carbs, and once during that session the pump worked as it should. But then the problem returned. Took the car for a test spin - ran great and when I got home I checked the pump again and of course, now it works as it should. So, now I am completely perplexed. Could this be caused by some type of electronic gremlin since it is a solid state pump?

Don
don scott

Don - Do you have an adjustment procedure for the all electronic pump? If not, send me an e-mail at SUfuelpumsp@donobi.net and I'll send you the procedure. I suspect that the diaphragm is short cycling due to marginal adjustment. Cheers - Dave
David DuBois

Ah, of course, an infernal electronic pump!
PaulH Solihull

This thread was discussed between 15/06/2012 and 16/06/2012

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