1975 Johnson 4HP 4R75, 4W75 Outboards Service Manual, Page 29Get this manual
RUBBER NSULATOR
bTwist leads counterclockwise off spark plugs and remove high tension lead anchorSee Figure 4-3cDisconnect throttle lever to armature linkinsert, Figure 4-3See
dUnscrew flywheel nut, (See Figure 4-4) and three flywheel screwsUse an appropriate flywheel holding tool when removing flywheel nutUsing flywheel puller (Special Tool #378103), pull flywheel from crankshaftSee Figure 4-5eLoosen the four Phillips head screws Remove armature plate from power headSee Figure 4-6Figure 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