How to Tell When It Is Time to Change the Spark Plug in a Lawn Mower

The spark plug in a typical two-cycle lawn mower engine supplies the short burst of electrical current to create combustion. Many Small-engine manufacturers typically recommend changing the spark plug every year at the start of the mowing season. It's good maintenance, along with changing the oil. If the engine has trouble starting or you notice other tell-tale signs of imminent problems, it may be time to change the spark plug even sooner than the annual replacement recommendation.

Spark plug wrench

Instructions

- 1
  Pull the insulated wire straight off the spark plug tip where it connects to the engine.
- 2
  Unscrew the plug from the socket using a spark plug wrench, twisting counterclockwise.
- 3
  Scrape your fingernail across the L-shaped wire on one end of the spark plug to check for scorching, dirt and corrosion. Inspect the plug's ceramic insulator for cracks or chips. If you see any signs of damage, replace the spark plug.
- 4
  Connect the rounded tip of the spark plug to the insulated engine wire but do not reinstall the plug. Set the connected plug on its side to watch the L-shaped wire while a friend pulls the mower's starter cord or turns the ignition key. If you do not see a spark or only a faint yellow spark, replace the plug.

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