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Fuel Pump Problems

Fuel Pump Problems

Can the list help me with a problem I have with the SU fuel pump on my 150? After numerous problems I replaced the original pump with an electronic conversion unit that fitted inside the existing bakelite cover, This worked fine for a while but recently decided to have an electronic "stop work" that has necessitated the fitting of a supposedly reconditioned contact type original SU pump. I have only had the car back a week from having this new pump fitted and have noticed petrol dripping from the lower lid of the pump body. On closer inspection it was apparent that a gasket had not been fitted between the lower lid and the body. As I had a spare gasket I removed the lower lid ( plus a large quantity of gunge - so much for a reconditioned pump! ) and fitted the new gasket. On reassembley the pump now sounds like a machine gun and is pumping no fuel. There appears to be fuel at the inlet union and even in the base of the lower lid when the six screws holding the lid are released a bit.There is fuel in the tank and the pump was working fine (apart for the slight leak) before I tried to fix it. Any ideas, as we are into summer here and I want to get on the road while most of the list are snow bound on the other side of the world! - Roger Herrick

2 things leap to mind: 1. the brass disc inside the fuel pump that acts as a one way valve to keep fuel moving in the forward direction may be stuck 2. 'grunge' in the pump maybe from the fuel tank causnig the disc to stick...theres a metal screen filter in the drain plug in the gas tank that may be missing or corroded, (also theres a metal mesh filter in the fuel pump itself that may be stopped up, but I dont think this is causing your problem as more than likely would cause the pump NOT to click) - Good Luck - David Drenzek

Could the gunge have come from your fuel tank? - George Badger

Pump clicking with the engine not running has no relation to a butterfly. If you let it go on clicking for a while and you smell gas or see some dripping on the floor, you obviously have a leak. ("leak" includes a needle valve with a float not sealing properly) If clicking continues and there is no leak, it is a pump problem. Either the diaphram is not OK or a check valve is not seating properly and is allowing gas to flow back to the tank. - Bruce Cunningham, '53 XK120 OTS

Thanks for the replies on my fuel pump problems. I ended up rebuilding a pump from the best parts of two spares and it now seems to be working OK. I think there was some dirt lodged in one of the valves under the top plate which needed the valve cage unscrewing and the valves cleaned. The only thing is that now the fuel pump keeps on beating (about once every one to two seconds) when the ignition is on but the engine is not running. Normally the fuel pump would beat furiously for 10 or 15 seconds and then stop until the starter button is pushed and the engine started. I don't think it is a fuel pump problem but may be a carburetter problem. If a throttle butterfly was not fully closing would that cause the problem? The reason this may be the cause is that the other weekend when I was returning from watching the local hill climb (C type Jaguar, Rileys, Lagondas etc.) I was accelerating hard in third gear into a sweeping corner and when I backed off the car kept accelerating flat out. With a great deal of tyre noise and smoke it just managed to make it around the corner (sideways) before it could be stopped by killing the ignition ( my 17 year son who was with me just thought I was showing off ! ). The throttle linkages were fine but I eventually found a 3 inch length of electrical wire ( ! ) in the base of the forward carburetter and jambed under the butterfly. Maybe the wire under the butterfly has meant that the carbs have been set up with one of the butterflys not seating properly and this is causing a air leak ( ? ) that means that fuel is being pumped even when the engine is not running. That is the best that my limited mechanical ability can come up with - no doubt the more mechanical will be able to come up with a better ( correct ) theory. - Roger Herrick

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