SAFETY FIRST: Protective gloves and eyewear are recommended at this point.
Inspect the spark plug porcelain for cracks or damage. Check the electrode for wear, fouling or deposits. The center and ground electrodes should have nice square edges. If they appear rounded, replace the spark plug. The spark plug porcelain insulator nose should be a light tan color, which can indicate how your engine is performing. For example, if the spark plug nose is white the engine may be running too lean, if the spark plug nose is dark the machine may be running too rich. Use a flat feeler gauge or a wire gauge to measure the gap between the ground electrode and center electrode. To change the gap, carefully bend the ground electrode.
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