Re: How does fuel pump work on '75 25hp?
As the piston moves up and down in it's cylinder, an alternating pressure / vacuum is formed below it in the crankcase. That alternating pressure / vacuum is applied to a thin rubber diaphragm in the fuel pump, flexing it back and forth. The opposite side of the diaphragm pulls fuel from the tank as it flexes one way, and pushes it on to the carburetor as it flexes the other way. A couple of check valves keep the fuel from flowing in the wrong direction.
