A built-in propulsion system includes an engine, a diversion unit with a diversion base and an exhaust pipe, and a propulsion unit. The diversion base is connected to the engine, having a water inlet, a water outlet, a diversion channel in communication between the water inlet and the water outlet, a shaft hole above the water inlet and an exhaust chamber behind the shaft hole. The exhaust pipe is fixed on the outer periphery surface of the diversion base in communication with the exhaust chamber. The propulsion unit includes a transmission shaft inserted through the shaft hole and connected to the engine, and an impeller located in the diversion channel and connected to the transmission shaft. The exhaust pipe is used to exhaust the exhaust gas of the engine to the outside of the diversion base to avoid the interference of the exhaust gas and the water flow.

An exhaust gas purification structure of an outboard motor includes an exhaust gas pipe that has an exhaust gas passage through which exhaust gas of an engine can flow; and a catalyst that is provided in the exhaust gas passage and purifies the exhaust gas by allowing the exhaust gas to pass through the inside thereof. The exhaust gas pipe includes a coolant flow passage allowing a coolant that cools the exhaust gas to flow therethrough. An exhaust gas bypass passage allowing the exhaust gas to flow without passing through the catalyst is formed between the catalyst and an inner surface of the exhaust gas pipe forming the exhaust gas passage.

An outboard motor is provided with: an engine cover in which a first outside air inlet port, an exhaust port, and second outside air inlet ports are formed; and a lower housing that is disposed below the engine cover. The engine cover is provided with a front guide and a rear guide that guide outside air, introduced respectively from the first outside air inlet port and the second outside air inlet ports into the engine cover, downward in the gravity direction.

A marine engine assembly for mounting to a watercraft is disclosed. The marine engine assembly has an engine unit, an exhaust system fluidly and a propulsion device. The engine unit includes an engine unit housing, an internal combustion engine and an air intake assembly. The air intake assembly, at least one combustion chamber, and the exhaust system together defining at least in part a gas flow pathway. A sealing valve is provided in the gas flow pathway. The sealing valve has an open position permitting flow of gas therethrough. The sealing valve has a closed position preventing flow of gas therethrough for sealing a portion of the gas flow pathway downstream of the sealing valve from a portion of the gas flow pathway upstream of the sealing valve. An air pump is configured for supplying air to the gas flow pathway downstream of the sealing valve.

An exhaust gas purification structure of an outboard motor includes an exhaust gas pipe that has an exhaust gas passage through which exhaust gas of an engine can flow; and a catalyst that is provided in the exhaust gas passage and purifies the exhaust gas by allowing the exhaust gas to pass through the inside thereof. The exhaust gas pipe includes a coolant flow passage allowing a coolant that cools the exhaust gas to flow therethrough. An exhaust gas bypass passage allowing the exhaust gas to flow without passing through the catalyst is formed between the catalyst and an inner surface of the exhaust gas pipe forming the exhaust gas passage.

An outboard includes a plurality of first branched pipes connected to a plurality of first exhaust ports and a plurality of second branched pipes connected to a plurality of second exhaust ports, respectively, wherein the plurality of first branched pipes are connected to a first collecting pipe and the plurality of second branched pipes are connected to a second collecting pipe. A connector connects the first collecting pipe and the second collecting pipe. The plurality of first branched pipes extend in a direction away from the connector in a plan view, and each includes a first exhaust pathway located farther away from the connector than the first collecting pipe is in the plan view. The plurality of second branched pipes extend in a direction away from the connector in a plan view, and each includes a second exhaust pathway located farther away from the connector than the second collecting pipe.

An outboard motor that significantly reduces or prevents discoloration around an exhaust opening includes an engine, a drive shaft, a propeller shaft, a housing, an exhaust passage, a water intake passage, and a valve. The exhaust passage guides an exhaust gas from the engine toward the discharge chamber inside the housing. The water intake passage guides water, which enters an inside of the housing, to the discharge chamber when a forward propulsive force is generated. The valve regulates passage of the exhaust gas at the first opening due to water pressure when a forward propulsive force is generated. The valve permits the passage of exhaust gas at the first opening due to exhaust pressure when a backward propulsive force is generated.

An outboard motor that significantly reduces or prevents discoloration around an exhaust hole includes an engine, a drive shaft, a propeller shaft, a housing, a discharge passage, and non-metal covers. The housing includes a discharge outlet to discharge an exhaust gas of the engine and the cooling water of the engine. The discharge passage guides the exhaust gas and the cooling water from the engine toward the discharge outlet. The covers are detachably attached to the housing so as to cover the discharge outlet and include at least one exhaust opening.

An outboard motor, including an engine having a cylinder containing a combustion chamber, an intake pathway connected to the combustion chamber, a piston disposed in the cylinder, a crankshaft connected to the piston, a fuel injection device connected to the intake pathway, and an ignition device connected to the combustion chamber. The outboard motor further includes a controller that is configured to receive a signal indicating an engine speed from a sensor, control the fuel injection device to suspend fuel supply and control the ignition device to suspend ignition, upon determining that the engine is in an over-revolution state, control the fuel injection device to release the suspension of the fuel supply upon determining that the engine has recovered from the over-revolution state, and control the ignition device to release the suspension of the ignition after lapse of a number of cycles of the engine since the release of the suspension of the fuel supply.

A built-in propulsion system includes an engine, a diversion unit with a diversion base and an exhaust pipe, and a propulsion unit. The diversion base is connected to the engine, having a water inlet, a water outlet, a diversion channel in communication between the water inlet and the water outlet, a shaft hole above the water inlet and an exhaust chamber behind the shaft hole. The exhaust pipe is fixed on the outer periphery surface of the diversion base in communication with the exhaust chamber. The propulsion unit includes a transmission shaft inserted through the shaft hole and connected to the engine, and an impeller located in the diversion channel and connected to the transmission shaft. The exhaust pipe is used to exhaust the exhaust gas of the engine to the outside of the diversion base to avoid the interference of the exhaust gas and the water flow.