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MG MGB Technical - Fuel Pump

I am having fits with the fuel pump on my 1971 MGB. I left the ignition key on overnight and naturally I ran the battery down. When I tried to start the car the fuel pump would only run for 1 or 2 seconds. I removed it, cleaned the contacts and reinstalled it. It runs fine now and pumps fuel from the pump to the hard line going to the engine, BUT I am not getting any fuel to the SU carbs. Did I burn up the 'pushing capacity" of the pump and is a new pump a fix? I was very careful to keep any debris out of the fuel lines, by the way.
Gordon A. Clark

Gord - The "pushing capacity" of the pumps comes strictly from the volute spring in the pump, not something that burns up. I would suspect that as the voltage got below 10 volts, the pump would no longe pull the diaphragm up far enough to flip the points over and was left with constant current through the coil, which will eventually burn out the swanping resistor inside the coil housing. This will cause the points to arc excessively and greatly reduce their life expectancy, but should not cause the pump to give the symptoms that you describe. Left wih full voltage on it, the pump should not be damaged by leaving it run all night (I run the pumps that I restore for 24 hours on my test stand as a final test and they don't even heat up above ambient temperature).

You say that you are getting fuel from the pump ot hte hard line going to the carbs, what about if you disconnect the line at the carb and turn the ignition on? Do you get fuel out of the open line at the carbs? If you do, then the pump is ok. If not then possibly something else in the pump may be damaged, but I couldn't guess what it might be without seeing the pump. Take a look at my SU fuel pump article at teh following web site: http://www.custompistols.com/cars/articles/dd_su_fuel_pumps_101.htm
There is a link at the end of the article to a write up of my SU fuel pump services and may be a better route to go than a new pump. Good luck - Dave
David DuBois

Gordon you may have a problem with the hose from the hard line to the carbys closing up (swelling shut)I have seen it many times and it may happen more with ethonal being used in higher %. DENIS
DENIS

This thread was discussed on 18/03/2004

MG MGB Technical index

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