Fresh Gas — Fresh gas (87 or higher octane rated) is critical to an engine’s performance. To fill the mower’s tank, use a clean funnel to draw gasoline from either a one- or two- gallon gas can. Plastic gas cans are a good choice because they won’t rust. If you own a five-gallon gas tank, dispose of it properly; the problem with a five- gallon can is that it provides the user with more than a 30-day fuel supply. Gas that is older than 30 days may affect engine performance. Moisture buildup and octane loss can lead to gum deposits in the engine’s fuel lines and carburetor, which can lead to poor engine performance.