How to Tell When Spark Plugs Are Bad in Riding Lawnmowers
- 1). Disconnect the wire lead from the spark plug. The round clip on the end of the wire pulls straight off the plug's terminal stud.
- 2). Unscrew the plug with the socket wrench by turning counterclockwise.
- 3). Spray plug cleaner on the L-shaped ground wire and center wire, which are at the opposite end of the terminal stud.
- 4). Scrub the end of the plug with a wire brush and inspect the exterior for cracks or other obvious damage in the ceramic insulator. If any part of the plug is cracked, scorched or blackened with burn marks, the plug is bad and must be replaced.
- 5). Adjust the plug gap to .03 inches, using the plug-gap tool. This is a standard plug gap for many riding mower engines. Consult the owner's manual for your particular mower to confirm the recommended gap.
- 6). Screw the cleaned plug into the socket and reconnect the lead wire to test operation. If the engine still hesitates or misfires, replace the old plug with a new one.
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