This video from Sears PartsDirect shows how to replace a spark plug on a lawn mower. The spark plug ignites the fuel in your engine’s cylinder. An old spark plug may be to blame if your engine runs rough or is hard to start. You should change the spark plug at the start of the mowing season when you give your mower its annual tune-up. If your spark plug isn’t firing and your engine won’t start, you can replace your spark plug using the steps in this video. Visit us at: http://www.searspartsdirec