1972 Johnson 4HP Outboard Motor Service Manual, Page 28Get this manual
RUBBER INSULATOR
Twist leads counterclockwise off spark plugs and remove high tension lead anchorSee Figure 4-3Disconnect throttle lever to armature linkSee insert, Figure 4-3dUnscrew flywheel nut, (See Figure 4-4) and three flywheel screwsUse an appropriate flywheel holding tool when removing flywheel nutUsing flywheel puller (Special #378103), flywheel from crankshaftSee Figure 4-5Loosen thefour Phillips head screwsRemove armature plate from power headSee Figure 4-6
Figure 4-2Hot and Cold Plugs plugsSpark plugs classified according to the temperatures at which they designed to operate, 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 motortrouble arise which might interpreted as carburetor difficultylow trolling speeds will tend to foul plugs due to the oil not burning from the However, at full throttle with hotter plugthe operating temperature too high, resulting in ignitionAn extreme temperature range will difficult to control with one plugSpark plugs furnished with the motor selected for average serviceSpark plugs recommended for the HP Models