How Do Yamaha Outboard Motors Work?

The outboard engine changed the way people used small boats all over the world. No longer tied to sail or oar, everyone from the local fisherman to the tourist on vacation could efficiently operate a boat without any special skills or knowledge. Today, the outboard engine is immensely popular for all kinds of different ships, but few people understand how they work and what makes these engines such a versatile choice for power. This article will give you an understanding of how a Yamaha outboard works and how Yamaha outboard manuals can be life-savers when it comes to keeping your motor running for years to come.

Physical Design Characteristics

All outboard engines share some common physical designs. You can think of an outboard motor as an engine on a swivel that mounts to the rear of a boat, called the transom. The mounting plate may come in various designs, but they all allow the engine to turn from side to side and rock vertically to lift the propeller out of the water. Larger engines use a separate motor to lift, while most smaller engines rely on leverage to manually rock the engine out of the water.

Top of the Engine

The top part of the outboard most often has a plastic or aluminum cover that protects the engine. Older designs will have engine and carburetor controls, while newer motors use computers to control the fuel flow and spark rate for optimal efficiency. You will find a folding handle used to orient the motor, including a twisting grip for throttle control. The engine will have either an electric starter button or a pull-cord. You’ll also find the gas cap on the top of the engine.

Lower Assembly

The spine of the outboard provides a sturdy and robust housing to connect the internal parts from the engine to the propeller shaft. At the base of the engine, you’ll notice that the metal housing has several fins, serving several functions. First, they reduce cavitation, which is the result of air being pulled into the water, reducing the efficiency of the propeller. Other fins act as rudders, helping to direct the flow of water for maximum thrust.

Internal Parts and Design

Before 2008, many manufacturers, including Yamaha, built two-stroke and four-stroke engines that used carburetors. However, the US Environmental Agency banned the sale of new two-stroke engines running carburetors and required manufacturers to meet emissions standards to prevent pollution.

Today, most outboard motors use a form of fuel injection meeting emissions standard requirements, and all two-stroke engines currently made are legal for sale. Luckily, although newer engines are more complex, they are still fairly easy to service using a Yamaha shop manual. Don’t have one yet? Take a look at eManualOnline. A good repair manual costs less than an oil change and will pay for itself in no time.

Two-Stroke vs. Four-Stroke Engines

The differences between a two-stroke and a four-stroke engine are complex and outside the scope of this article. Still, if you’d like to know more, a Yamaha OEM service manual describes how each engine works in depth.

But in simple terms, a two-stroke engine typically requires oil added to the fuel to lubricate the engine’s internal parts, which has a negative effect on emissions. However, a two-stroke engine produces more torque than a four-stroke one. A two-stroke engine is also a more straightforward design that requires less maintenance.

How the Motor Works to Make Power

In general, outboard motors are configured so that the pistons operate horizontally. The motor’s orientation allows for the rotational force of the crankshaft to be transmitted directly to the driveshaft. The driveshaft connects the crankshaft output to the prop shaft gear cluster. As the drive shaft rotates, gears in the engine’s bottom transmit the rotational force of the driveshaft into counter-rotational force to drive the propeller. A set of gears allows the prop to run either forward or reverse in themost simple configuration.

Modern Fuel Injection and Timing

In the old days, the operator of an outboard engine would need to trim the spark and fuel delivery as the engine speed changed. This variation allowed the engine to attain higher operating speeds without starving for fuel or “pinging,” a condition caused by spark plugs firing at the incorrect time.

Today, these functions are controlled by computers, much like the ones on your car engine. Rather than relying on atmospheric pressure changes needed by carburetors, an electronic fuel injection system delivers the correct amount of fuel to the cylinders at the right time, making a more powerful and efficient engine at all RPMs.

How a Yamaha Outboard Engine Makes the Boat Move

If you think of the propeller as a regular fan, you’ll get a good idea of how the outboard works. Like in a fan, the motor turns the propeller. The faster the propeller turns, the faster the boat can go. When the boat is in the water, the propeller must be below water to work. Unlike your house fan, though, the propeller isn’t large enough to create force when it isn’t in the water.

This is a condition called cavitation, and it is often caused by an improperly set up engine that allows air to be pulled into the stream of water pushing away from the prop. A Yamaha service manual can show you the right way to adjust the motor’s position for your boat.

A larger propeller or one with multiple vanes offers more performance but requires more power and weighs more. Heavier components are necessary as the power of the motor increases, which makes it impractical to put large outboards on small boats. When you see a boat sitting with the bow high in the air while at rest, that indicates the motor is too heavy, which could create dangerous conditions like flipping over.

Final Thoughts

Outboard motors are not excessively complex designs, but they do require at least a basic understanding of how they work so you can keep them running perfectly at all times. Many manufacturers are making outboard engines, but few are as reliable, efficient, and powerful as Yamaha’s. You can learn more about these great engines from Yamaha outboard service manuals.

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