1968 Evinrude Big Twin, Big Twin Electric, Lark 40 HP Outboards Service Manual, Page 34Get this manual
spark plugsSpark plugs are classified cording to the temperatures at which they are designed to operate, or COLDSee Figure 4-2Selection of the correct spark plug depends the type of service to which it is subjectedUnless the spark plug is properly suited to the motor, trouble arise which might interpreted as carburetor difficulty Very low trolling speeds will tend to foul plugs due to the oil not burning from the coreHowever, at fuH throttle with hotter plug, the operating temperature too high, resulting in pre-ignitionAn extreme temperature range wiH difficult to control with one plugSpark plugs furnished with the motor are selected for average serviceSpark plugs recommended for the 40 motors are: 1Champion: J4J 23Auto-Lite: Figure 4-4Pulling Flywheel Remove armature link spring and washerLoosen four Phillips head screws attaching magneto armature plate to power headSee Figure 4-6Lift magneto assembly from power head LOCKING