Flying Horse 2-Stroke/4-Stroke Motorized Bicycle Inline Fuel Filter &ndash; Gas Bike Fuel Filter The Fuel Filter helps keep dirt and big deposits from entering the carburetor when your bicycle engine fuel is flowing Installation is a breeze: cut your fuel line in half. The top valve goes in to the fuel line coming from the tank, and the bottom valve goes in to the fuel line coming from the carburetor. Fasten if needed, and you're ready to ride