2000-2005 Yamaha F40B Outboard Service Manual, Page 456Get this manual
IGNITION SYSTEM
1Check: Spark plug cap Loose connection Cracksdamage
CHECKING THE SPARK PLUG CAPS
TightenReplace
Replacement steps (1) To remove the spark plug cap turn it cou nterclockwise(2) To install the spark plug cap turn it clockwise until it is tight
2Measure: Spark plug cap resistance Out of specification ReplaceSpark plug cap resistance