1976 Johnson 4HP 4R76, 4W76 Outboards Service Manual, Page 29Get this manual
RUBBER INSULATOR
1 IIII:;;I!;;]I NOTE
servicing only the breaker points, condensers, and coils, these can be checked and replaced without removing the armature plate
cIf necessary to replace the high tension leads, twist leads counterclockwise off spark plugs and remove high tension lead anchorSee Figure 4-3dDisconnect throttle lever to armature linkSee insert, Figure 4-3eLoosen the four Phillips head screws retaining the armature plateRemove armature plate from power headSee Figure 4-6
Figure 4-2Hot and Cold Plugs at which they are designed to operate, HOT or COLDSee Figure 4-2Selection of the correct spark plug depends on the type of service to which it is subjectedUnless the spark plug is properly suited to the motor, trouble may arise which might be interpreted as carburetor difficultyVery low trolling speeds will tend to foul plugs due to the oil not burning from the coreHowever, at full throttle with hotter plug, the operating temperature may be too high, resulting in preignitionAn extreme temperature range will be difficult to control with one plugSpark plugs furnished with the motor are selected for average serviceSee Section 2, Specifications