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Posted by johnd [71.125.161.79] on Sunday, February 12, 2012 at 07:12:15 :
In Reply to: Fuel pump posted by Robert [68.96.73.106] on Saturday, February 11, 2012 at 15:26:00 :
If the diaphram doesn't have a hole in it, you probably have dirt holding one of the check valves open. The check valves are inside the pump housing. One lets the fuel come into the pump when the diaphram raises, but shuts when the diaphram lowers. This prevents the fuel from running back into the tank instead of towards the carb.
The other check valve opens to let fuel go to the carb, but closes when the diaphram is raising to suck fuel from the tank.
If you visualize this flow, you can see that it's possible for the fuel to make one step forwards, and another backwardsb- keeping it from going to the carb- if either check valve is held open.
You can prove all of this by taking both fuel hoses off, and putting a few feet of clear hose on both the inlet and outlet and pumping by hand from a small container. You will actually see the fuel moving.
Another possibility is that the spring is broken that returns the arm after the cam lobe has moved it up.
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