How to Replace a Fuel Filter on a Lawn Mower - Home Guides How to Replace a Fuel Filter on a Lawn Mower. One of the key factors of a smooth-running lawn mower engine is clean fuel. Therefore, a replaceable filter is installed in the fuel line to keep dirt and debris out of the fuel mix. When the filter has done its job, you must replace it. Annual replacement as part of your regular tuneup routine is.. How to change a fuel filter in small engines? | Briggs The fuel filter will be located either inside the fuel tank or fitted into the fuel line between the tank and the fuel pump. Some engines have internal, non-serviceable fuel filters. If you are unsure of where your fuel filter is located, refer to your Briggs & Stratton® Engine Operator's manual to determine the location.