Carburetor Diaphragm The Heart of the Fuel Pump

This diaphragm is not sold alone. It comes with a spring and a ring, and the three together are the heart of the fuel pump. The 270026 is a carburetor diaphragm used across the small horizontal shaft engines of three to five horsepower, the kind that runs mowers.

What does the diaphragm do? This kind of carburetor is a pump type, with no separate fuel pump and no primer bulb. The diaphragm is the pump. It flexes back and forth and draws fuel from the tank into the carburetor. When the diaphragm stops moving, the fuel stops coming, and the engine cranks fine but will not start, with no smell of fuel.

Why does it come with a spring and a ring? The spring drives the diaphragm and gives it its bounce, and the ring seals the edge. The three work as one. Fit the diaphragm without the spring and the ring and it still will not pump, so they are sold together as a set.

What is the part like? The diaphragm is a black rubber sheet, with a long opening cut so the fuel passage can pass through, and a few small holes around the edge for the bolts. The spring is metal, and the ring is a thin metal ring. The diaphragm, the spring and the ring make up the complete fuel pump.

How to replace it? Take the carburetor apart, and out come the old diaphragm, the old spring and the old ring, swapped one for one, with the diaphragm the right way up, cut out side toward the fuel passage. When fitting it, check that the spring is not snapped and the ring is not deformed.