I Can Not Get a Spark for My Lawn Mower

Old Spark Plug

• As the gas burns up inside the cylinder, a small fraction of the gasses cools off and collects on any exposed area. These carbon deposits will collect on the metal, gapped end of the spark plug. When the carbon covers the tip, the spark plug will no longer discharge the spark properly. Pull the rubber boot off the tip of the spark plug and unscrew the plug using a socket wrench. If the tip on the plug looks black, replace it with an identical model.

Loose Boot

• A rubber boot sits at the end of the HT lead wire. Inside this boot, a small metal capsule connects the spark plug to the wire. When the boot gets pulled off improperly, with too much force, the metal capsule can get dislodged or come loose. If the capsule is loose, the voltage won't transfer to the plug. The entire boot may also come loose if the boot was pulled off at an awkward angle. Check the boot for any looseness and damage. Ground the wire on a metal point on the engine block if proceeding further with ignition repairs.

Loose Electrical Wiring

• For the lawn mower to continue generating a spark, the voltage needs to make a continuous circuit throughout the ignition system. If this spark gets prematurely grounded, the added resistance can translate into a lost spark. Outside of performing a full diagnostic test on the electrical system with a voltmeter, the only thing the operator can do is to inspect the conditions of the electrical wiring carefully, paying special attention to the connecting points. Replace any damaged, loose or frayed wires.

Ignition Module Issues

• The ignition module on a lawn mower produces a spark through an electric coil that acts much like a capacitor in a radio or TV. This coil builds, holds and fires off the electrical charge. The electrical energy, however, originates at the flywheel, which builds up energy. As the flywheel spins, the magnets on the outside help the coil to build and eventually fire the spark. If the magnets are blue or discolored, replace the entire flywheel. If the magnets are in working order, a service professional will need to inspect and possibly replace the ignition module.