Abstract: To provide an output shaft structure of a personal watercraft, which is capable of enhancing the durability of the engine. An engine is mounted on a watercraft body with a crankshaft extending in the longitudinal direction of the watercraft body. A shaft of a propulsion device is coupled to a rear end of the crankshaft in such a manner as to be disposed on an extension of the crankshaft. The crankshaft is supported by an engine case via plain metal. An output shaft is provided separately from the crankshaft and is coupled to the rear end of the crankshaft. The shaft of the propulsion device is coupled to the rear end of the output shaft. The output shaft is supported by the engine case via rolling bearings immovable in a thrust direction. A spline is formed on or in each of the rear end of the crankshaft and the front end of the output shaft, and a spline to be engaged with these splines is formed in or on an inner surface of a connection pipe.

Abstract: To provide an output shaft structure of a personal watercraft, which is capable of enhancing the durability of the engine. An engine is mounted on a watercraft body with a crankshaft extending in the longitudinal direction of the watercraft body. A shaft of a propulsion device is coupled to a rear end of the crankshaft in such a manner as to be disposed on an extension of the crankshaft. The crankshaft is supported by an engine case via plain metal. An output shaft is provided separately from the crankshaft and is coupled to the rear end of the crankshaft. The shaft of the propulsion device is coupled to the rear end of the output shaft. The output shaft is supported by the engine case via rolling bearings immovable in a thrust direction. A spline is formed on or in each of the rear end of the crankshaft and the front end of the output shaft, and a spline to be engaged with these splines is formed in or on an inner surface of a connection pipe.

Abstract: The expected performance of a jet-propelled boat is maintained, exhaust control valves are controlled and driven in an improved accuracy on the basis of the traveling speed of the jet-propelled boat. Thus, the fuel consumption is improved and the exhaust gas is purified. A two-stroke cycle engine drives a jet propulsion unit to make the jet propulsion unit suck in water and jet water therefrom to propel a hull of the boat. An exhaust control valve is disposed near the exhaust port of the engine to change the opening ratio of the exhaust port according to the operating condition of the engine. A driving mechanism for driving the exhaust control valve includes a hydraulic actuator. The power of water jetted by the jet propulsion unit represents the traveling speed of the jet-propelled boat accurately.

Abstract: To provide a structure for attaching exhaust control valves near exhaust ports in a two-cycle engine, the exhaust control valves variably controlling open areas of the exhaust ports. The cavity for receiving the exhaust control valves is formed near the upper edges of the exhaust ports on the cylinder block. The holder member is interposed between the cylinder block and the exhaust manifold, is attached to the pivot for supporting the exhaust control valves. A flange is provided for connection with the cylinder block. Therefore, the exhaust control valves are disposed near the upper edges of the exhaust ports. It is not necessary to form bearings on the cylinder block using a complicated process. Complicated parts such as bearings are collectively formed on the holder member that is independent and compact and easily machined. The pivot extends across the exhaust passages that are formed downwardly in order to detour around the pivot.

Abstract: A method of lubricating a two-cycle internal combustion engine, which is capable of preventing blow-by of an air-fuel mixture in a combustion chamber, is provided for increasing fuel consumption and purifying exhaust gas. Lubrication of a valve portion and a sliding portion of a cylinder bore to a piston is improved so as to enhance maintenance performance and further improve fuel consumption. The method for lubricating a two-cycle internal combustion engine in which a control valve is disposed, in communicating passages for communicating a combustion chamber to a chamber portion adjacent to the combustion chamber, wherein the oil is supplied to bearing portions of the control valve for lubricating the bearing portions, and also the oil permeates through the communicating passages to be supplied to a sliding portion of a cylinder bore to a piston by an injection flow of the fuel or the air-fuel mixture, and lubricates the sliding portion.

Abstract: A two-cycle engine of the spark ignition type is provided wherein a mixture in a combustion chamber can be compressed and self-ignited at least in a low load operation region to effect an activated heat atmosphere combustion. In a transition operation region between the activated heat atmosphere combustion region and an ordinary spark ignition combustion operation region, the mixture can be ignited by a spark ignition at a timing earlier than the spark ignition timing in the ordinary spark ignition combustion operation region to stabilize the combustion condition and eliminate abnormal combustion noise and the harmful effects of heat. A throttle valve opening of a throttle valve manually operated is detected by a throttle valve opening sensor formed from a potentiometer or the like while an engine speed is detected by an engine speed sensor, and they are inputted to a CPU. The CPU operates in accordance with a control graph of FIG.

Abstract: A combustion controller for an internal combustion spark ignition type two-cycle engine includes exhaust passage opening ratio adjusting means for adjusting an exhaust passage opening ratio, wherein the exhaust passage opening ratio adjusting means is driven to adjust the exhaust passage opening ratio at a value corresponding to an engine speed and a throttle valve opening ratio at least in a low load operational area. And fresh mixture in a combustion engine is self-fired with a firing timing desirable for operation of the engine. In this engine, the combustion controller includes ignition timing adjusting means for adjusting an ignition timing; abnormal combustion detecting means for detecting abnormal combustion in the combustion chamber; and control means for controlling the exhaust passage opening ratio. The ignition timing at respective values eliminates the abnormal combustion on the basis of the detection signal from the abnormal combustion detecting means.