Abstract: It is intended to provide an exhaust control system in a two-cycle internal combustion engine capable of suppressing the occurrence of irregular combustion when an opening timing of an exhaust port is set to a maximum delay timing, thereby improving the combustion stability and affording a high engine output when the opening timing of the exhaust port is set to a maximum advance timing. In the exhaust control system, an exhaust control valve has valve elements movable between their maximum projected positions at which a maximum delay timing of the exhaust ports is set and their maximum retracted positions at which a maximum advance timing of the exhaust ports is set. The valve elements are provided with control surfaces, that face a cylinder bore at the maximum projected positions of the valve elements to close upper port portions of the exhaust ports.

Abstract: It is intended to provide an exhaust control system in a two-cycle internal combustion engine capable of suppressing the occurrence of irregular combustion when an opening timing of an exhaust port is set to a maximum delay timing, thereby improving the combustion stability and affording a high engine output when the opening timing of the exhaust port is set to a maximum advance timing. In the exhaust control system, an exhaust control valve has valve elements movable between their maximum projected positions at which a maximum delay timing of the exhaust ports is set and their maximum retracted positions at which a maximum advance timing of the exhaust ports is set. The valve elements are provided with control surfaces, that face a cylinder bore at the maximum projected positions of the valve elements to close upper port portions of the exhaust ports.