Abstract: A two-cycle engine includes a port timing control device for varying a timing of the opening of an exhaust port by a piston. The port timing control means includes a first valve mounted within an exhaust passage adjacent to an upper end of the exhaust port and having a port timing control surface, a second valve mounted on a cylinder block between a cylinder head and the first valve and having a closure surface, and an urging member acting on the second valve to always urge it against the first valve. The first valve is operable to be angularly moved about an axis generally perpendicular to the axis of a cylinder into and out of an extended position where the control surface is disposed slightly below the upper end of the exhaust port to close a part of the exhaust port. The second valve is movable along a generally straight path into and out of an extended position where the closure surface closes that portion of the exhaust port lying between the upper end of the exhaust port and the first valve.

Abstract: An exhaust system of a two-cycle engine mounted on a motorcycle is provided with a subchamber branching off from the exhaust pipe. The subchamber is disposed by utilizing a so called dead space in the frame of the motorcycle, particularly in a position in front of the engine and between a pair of cradle pipes of a body frame on which the engine is mounted. With this arrangement, it becomes possible to layout the position of the subchamber without altering the configuration of the body frame, and there is further advantage that the subchamber is well protected by the structural members.

Abstract: A kick-starter device having a cam connected to a kick-starter spindle. The cam has two cam parts, one of which is a large diameter part for a decompression operation, and the other of which is a small diameter part for resetting operation. The cam is rotated by the driving force of the kick-starter spindle. A cam follower is guided by the large diameter part of the cam rotated by a kicking operation at the time of starting and operates a decompression mechanism, whereby the decompression operation is made in response to engagement of the cam follower with the large diameter part of the cam only within the range of a fixed angle of rotation of the kick-starter spindle.