If your mower is hesitating, sputtering or simply won’t start, there is a good chance bad gas is the problem. Volatile compounds allow gas to burn. As these compounds evaporate, gas becomes less combustible and eventually turns into a gummy, varnishlike substance. Empty gas tanks and gas cans sometimes contain old gas deposits that break loose when new gas is added. These loose particles can clog the fuel line, fuel filter and carburetor. It is important to remove all traces of bad gas before refilling the tank.

Step 1: Set the mower on cinder blocks or a pair of saw horses to allow easy access to its underside. Avoid tipping the mower at all costs. When a four-cycle mower is tipped, oil runs from the oil reservoir into other parts of the motor, creating a whole host of problems. If you must tip a mower, tip it backward rather than to the side

Step 2: Disconnect the spark plug wire from the spark plug by pulling the rubber cap up and off the top of the plug.

Step 3: If you are lucky, there should be a fuel line running from the gas tank to the carburetor. If this is the case, set a plastic container beneath the tank, disconnect the fuel line from the carburetor and allow the fuel to drain into the plastic container.

Step 4: If you are unable to drain the gas from the fuel line, use a kitchen turkey baster or a hand siphon pump to remove as much a gas as possible from the tank.

Step 5: Use rags to soak up any remaining gas and residue from the bottom of the tank.

Step 6: Add a little fresh gas to the tank and, if possible, slosh it around. Drain the new gas into the plastic container, along with the rest of the bad gas.

Step 7: Allow the tank to dry completely. Reattach the fuel line and the spark plug wire.

Step 8: Check to see that the air filter is clean and the oil reservoir is full.

Step 9: Place the mower on the ground, refill the tank with clean, fresh gas and start it up.

There may be some additional sputtering for a while until the mower burns through the fresh gas and the bad fuel is flushed out of the carburetor and fuel filter.