Operating a Motor Boat
Motor Operation
The outboard motor is a spark ignition engine. Fuel from the fuel tank enters the carburetor where it mixes with air in a given proportion. From the carburetor, the gas mixture enters the cylinder. In the cylinder, a spark plug emits a spark that ignites the mixture, triggering an explosion that drives the piston. This sets in motion a crankshaft (or drive shaft) linked to the piston by a connecting rod. Successive explosions in the cylinder cause the crankshaft to turn and a gear assembly activates the propeller.
The internal temperature of a spark ignition engine is over 3200 Celsius (4000 F). Therefore, the motor must be cooled. Outboard motors are cooled by water.
While the motor is running, water is drawn in through openings located at the base of the motor (see Figure 2.1, no. 14) under the anti-cavitation plate. Water flows around the cylinders before being flushed out into the surrounding body of water through a cooling system control jet. It exits through an orifice located near the cylinder head (see Figure 2.1, no. 1).
Most outboard motors are two-stroke engines; four-stroke engines also exist.
Two- and four-stroke engines differ in the way that lubricating oil enters the cylinders. In a two- stroke engine, oil is added to fuel in the tank itself (manufacturers specify how much oil to add to the fuel). However, some two-stroke outboard engines have two tanks: one for gas and another for oil. The oil and gas mix automatically before reaching the cylinders. In a four- stroke engine, oil is added through a separate opening located near the drive shaft. Too little oil can cause the metal to overheat and damage the motor.
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