Your fuel pump is operated by the vacuum of the compression of the motor. The vacuum operates a diaphragm contained within the fuel pump to release fuel. The motor creates suction everytime the piston is on its down stroke after the Exhaust stroke.Click to see full answer. Then, how does a diaphragm type fuel pump work?Diaphragm pumps use a composite membrane, which flexes up-down over a fuel bowl. The bowl has an input and an output, each with a check valve in place to ensure a one-way motion of fluid. As the diaphragm moves up, it creates a vacuum, pulling fuel from fuel tank into the fuel bowl.Additionally, how does a small engine vacuum fuel pump work? Fuel from the tank is piped to the inlet side of the pump, the pump has a diaphragm that is activated by vacuum or mechanical linkage, on vacuum pumps the it is either getting vacuum from the valve cover or on the oil dip stick, this forces the fuel to the carburetor. They are also called pulse pumps. One may also ask, how does a vacuum operated Petcock work? The way a vacuum petcock works is the vacuum pulls the diaphragm back, compressing a spring and releasing pressure on a ball or some other sort of valve, this allows fuel to flow around the ball and to the carb.Should a lawn mower fuel filter be full?You ok as long as fuel is being sucked through the system, but you should see fuel in the filter at some point. It may take a few days to fill up and if it doesn’t it can cause fuel starvation problems soon.