How to Test a Spark Plug to See If It’s Working

Remove the spark plug wire

• Remove the shroud that covers the spark plug on a chainsaw or outboard motor. Small engines on lawn mowers and lawn tractors usually do not have spark plug shrouds.
• Pull the ignition wire off the end of the spark plug. Don’t just yank on the body of the wire itself, though, because this can cause damage. Reach down around the sides of the spark plug and gently pull on the end fitting of the wire that sits over the top of the spark plug.
• If the cap and ignition wire don’t want to come off, rotate the rubber fitting one way or the other as you pull.

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