Abstract: A two-cycle internal combustion engine including a carburetor, a crankcase provided with a crank chamber and a suction port, an insulator attached to the crankcase and provided with a suction passage for introducing an air-fuel mixture from the carburetor to the suction port, and a reed valve whose proximal end portion is fixed to the insulator so as to allow a free end portion thereof to be optionally press-contacted with the downstream side end face of the insulator, thereby opening or closing the suction passage, wherein a rib is formed on a portion of the downstream side end face of the insulator which is in the vicinity of the free end portion of the reed valve in such a manner as to protrude into the suction port.

Abstract: To avoid stalling of a two-stroke internal combustion engine as its orientation is changed upon a change of direction in which a working machine such as a chain saw is held, non-atomized fuel is prevented from flowing precipitously into the combustion chamber of the engine. The engine comprises a crank case forming a crank chamber which has an intake port opening into the crank chamber, and a flow control feature at the circumferential inner surface of the crank chamber in the vicinity of the intake port for retarding flow of non-atomized fuel.