1990 Johnson Evinrude "ES" 9.9 thru 30 Service Manual, P/N 507871, Page 103Get this manual
Spark Plug Information The spark plugs should be removed and examinedA spark plug should be replaced if the electrodes are badly worn, if it has cracked insulator, or is badly fouledBefore installing the spark plug cover, apply light coating of OMC Triple-Guard grease to the ribbed portion ofthe spark plug ceramic and to the opening of the spark plug coverThis will help prevent corrosion of the spring terminal and the spark plug which can cause high tension arcing
Spark Plug, Champion