The basics on how a outboard engine works.


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Engine Power and Design

  • Outboard boat engines work like a regular lawnmower engine or car engine in some cases. They run in either a two-stroke (like most lawnmower engines) or four-stroke process. This means that the engine takes two or four “strokes” to complete the cycle. In two-stroke engines, the downward cycle and upward cycle of the piston complete all four stages of ignition in the engine: it will intake gas and air, compress it, fire a spark and ignite, and then exhaust the fumes. In a four-stroke engine these four steps are separated into different cycles, and occur during stages of the upward and downward stroke of the piston. So, fuel and air intake occurs at one stage, compression at another, spark and ignition on the third and exhaust on the final step.

Engine Operation

  • An outboard motor operates on one of the two above principles. It is housed inside a cover and is connected to a vertical drive shaft that will spin the propellers of the engine. When started the engine begins its cycle. The drive shaft is always spinning, but a clutch will engage the shaft to the propellers. When this happens the outboard is sending drive to the boat and moving it forward. The force of this transfer is absorbed by the water around the boat and the transom, which houses the outboard engine.

Exhaust and Cooling

  • Outboards are like a typical engine, however they are cooled by water. This water is flushed through the outboard from the boat itself. Since they do not have radiators, this is a necessary part of their design and operation. Most all of the exhaust of an outboard is expelled through the bottom fin of the propeller. This is why there are bubbles coming up from the propellers when the boat is started. This exhaust is also mixed with some water from the cooling system. It cycles through the engine and then is pushed up with the exhaust. The system never needs coolant because it takes water from the lake or ocean that surrounds it.


  • Since the cooling comes from water it means there is more vapor inside the outboard motor. This is why many marine outboard motors have problems with gas that contains ethanol. It reacts with the vapors to cause damage to engine parts. Most outboards need a solution to help prevent this damage, and that mixture is usually added to the fuel and then run through the machine.

    If your having problems with your outboard engine your in luck Outboard Clinic works on all major lines such as Suzuki , Yamaha , Mercury , Polaris , Honda , Johnson , Evinrude , seadoo. To get a estimate or learn how to fix your engine feel free to drop us a email and or phone call.


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