1976 Evinrude 200 HP Outboards Service Manual, PN 5199, Page 65Get this manual
DESCRIPTION The power head consists of the cylinders, pistons, connecting rods, crankshaft, and crankcaseThe power head has two banks of horizontally-mounted cylinders in "V" formation 90 apartEach cylinder delivers one power impulse per crankshaft revolution, thus giving one power impulse at every 60 degrees of crankshaft rotation
the crankcase where fuel and air mixture has been induced by carburetionThe downward motion of the piston compresses this mixture in the crankcase and forces it through the intake ports into the cylinderThe in rushing charge of the fuel-air mixture helps in ejecting the last of the exhaust gases from the cylinderSee Figure 5-1A, Fuel Intake and ExhaustAs the piston begins its upstroke, it closes the intake and exhaust ports and begins to compress the fuel and air mixture trapped in the cylinderThe upward travel of the piston also reduces the pressure in the crankcase compartmentThe resulting suction opens leaf valves which admit additional air and fuel from the carburetor into the crankcase, thus preparing the next cylinder chargeSee Figure 5-1B, Compression StrokeAt the top of the piston stroke, the compressed fuelair mixture is ignited by timed spark and the cycle begins anewIn an outboard motor engine running at full throttle, this cycle may be repeated 5000 or more times every minuteSee Figure 5-1C, Power Stroke