Check the color of the ceramic insulator of the center electrode. A uniform light brown color indicates good engine condition and the correct heat rating.
Check the centre electrode for wear. If it is worn or vitreous, change the spark plug.
Check the spark gap. This must be 0.6 mm/0.023 in.
Caution! To adjust the gap, lever the side electrode very carefully. A gap which is too large or too small will cause starting difficulties and idling problems.
Carefully clean the electrode and insulator with a small wire brush and check the state of the sealing washer.
Carefully clean the spark plug hole in the cylinder head, making sure that no dirt or other object can fall into the combustion chamber.
Screw the spark plug in by hand until the washer is seated against the top of the hole.
When the spark plug is finger tight, use a plug wrench to tighten to the recommended torque.
Caution! Do not use spark plugs with an unsuitable heat rating or incorrect thread length. Spark plugs must be properly tightened. Spark plugs that are not correctly tightened will overheat and may cause engine damage.