Why Does My Lawn-Boy Walk-Behind Mower Run for a Minute and Stop?

Vapor Lock

• The fuel system on a Lawn-Boy mower uses the pressure generated by the spinning crankcase to move fuel from the tank to the carburetor. As the crankcase spins, the diaphragm in the fuel pump squeezes and relaxes, bringing fuel into the carburetor with every motion. However, if the pressure inside the carburetor drops below the pressure inside the fuel tank, the fuel will stop flowing. Vapor lock occurs when a gas cap can't vent the pressurized gases in the tank. Clean the fuel cap with a brush and soapy water, or replace it.

Clogged Fuel Filter

• Before the fuel can exit the tank and enter the carburetor, it needs to pass through the fuel filter. This filters our any unwanted debris that might damage the carburetor and the piston. However, if the fuel filter gets clogged, the fuel stops flowing, and the engine shuts off. This occurs as particles such as grass or dirt float around in the fuel. When the fuel gets sucked into the carburetor, the particles lodge against the filter and shut down the engine.

Bad Fuel Hoses

• Two plastic fuel hoses carry gas from the tank to the carburetor and back again. These two hoses need to stay clear of any obstruction to allow enough gas into the carburetor to keep the mower running. Impurities in the fuel gradually layer onto the hoses, eventually clogging them to the point where the mower runs for a minute and then stops. Replace both of these fuel hoses at least every other season, at a minimum.

Dirty Carburetor

• As the fuel enters the carburetor, it moves through the measuring chamber and into the mixing chamber. An inlet needle, through a spring, raises the inlet lever, allowing gas to flow into the mixing chamber. However, if the inlet needle or lever gets stuck partially closed and stops responding with the engine, the fuel cycle will probably run for a minute and then shut down the engine as the fuel gets used up. Remove and disassemble the carburetor. Clean out the inlet passage, bore and inlet needle and lever arm.