How to Change a Lawn Mower Spark Plug (Plus Signs It's Bad)

  Quick Answer To change a lawn mower spark plug: pull the spark plug wire, remove the old plug counterclockwise with a spark plug socket (usually 3/4 inch or 13/16 inch), check the new plug's gap against your manual's spec , thread it in by hand to avoid cross threading, then tighten snug plus about a quarter turn . Replace the plug every season or every 100 hours . A black sooty plug means the engine is running rich ; a wet plug means flooding or no spark; a white blistered plug means running lean. In This Guide Signs Your Lawn Mower Spark Plug Is Bad How Often to Change a Lawn Mower Spark Plug Step by Step: Changing the Plug Reading the Old Plug: What the Color Means Buying the Right Plug Frequently Asked Questions The spark plug is the cheapest part on your mower and the most informative: a few dollars, ten minutes to change, and the old plug comes out carrying a written report on how the engine has been running. Our technicians replace plugs on nearly every service visit ...