1974 Johnson 40 HP Outboard Motors Service manual, Page 44Get this manual
DESCRIPTION The power head consists of the cylinders, pistons,
rods, crankshaft, and crankcaseThe power head
Fuel Intake and Exhaust
has two horizontally ounted cylindersAlternate firing order is used so that each cylinder delivers one power impulse per rankshaft revolutionSee Figures 5- and 5-2
EXHAUST PORT EXHAUST GASES
INTAKE PORT
THEORY OF OPERATION
Two-cycl engines used on outboard motors equire only two piston trokesone up, one down, to effect