Gasoline can leave behind a gummy deposit in your carburetor and fuel line, especially if your mower has not been started and run for a while. This is especially true if gasoline has been left in a fuel tank or carburetor over a long winter. If these gummy deposits are not removed, your engine may run poorly--or not run at all. The fastest and simplest way to clean your lawn mower's fuel system is to add lawn mower fuel system cleaner to your gas tank.
Purchase a fuel system cleaner designed specifically for lawn mowers.
Fill a gas can with 1 gallon of new, clean gasoline. Measure the exact amount of lawn mower fuel system cleaner recommended by the manufacturer (often 2 tablespoons per gallon of gas) and add it to the gallon of gas. Dump the gas with the fuel system cleaner into your mower's fuel tank. If your mower's fuel tank already has fuel in it, add enough additional fuel system cleaner to approximate the manufacturer's recommended strength.
Start your engine and allow it to warm up for two minutes. Mow your yard using the throttle setting you normally use. Mow until you have run almost a full gallon of gas through your mower's engine and fuel system. Add clean gasoline without fuel system cleaner to your tank once the tank is almost empty.
Add the manufacturer's recommended amount of lawn mower fuel system cleaner to your mower's gas tank once every 30 to 60 days to keep your system clean.