Abstract: Cylinder head construction defining a hemispheric combustion chamber which includes a guide wall provided to impart swirl to the incoming air-fuel mixture. The guide wall facing the intake port defined by the cylinder head construction and generally parallel to the line of action of an intake valve provided in the intake port has a height greater than the maximum lift of the intake valve, and decreases in width in the direction of opening of the intake valve. In addition, the size of the area and the position of the guide wall relative to the intake port and the intake valve are maintained in specific ranges, and thus the construction not only permits efficient ignition of a lean air-fuel mixture, but at the same time causes only a slight drop in engine performance.

Abstract: Cylinder head construction defining a hemispheric combustion chamber and including a guide wall facing an intake port to impart swirl to an incoming air-fuel mixture and permit use of a lean air-fuel mixture. The position of the guide wall relative to the cylinder center and relative disposition of the guide wall and a spark plug are made such that although the guide wall is effective in imparting swirl, a flame front may be efficiently propagated to all parts of the combustion chamber subsequent to ignition of the air-fuel mixture therein, whereby provision of the guide wall does not result in increased emission of hydrocarbon compounds in exhaust gas or formation of carbon deposits in the combustion chamber.

Abstract: Four cycle internal combustion engine including an intake passage leading to an intake port formed in the cylinder head. The intake passage comprises a first passage section connected to the intake port with an inclination so that intake air-fuel mixture is introduced into the engine working chamber with a circumferential velocity component to produce a swirl in the working chamber. The intake passage further includes a second and third sections which together with the first section form a meandering substantially S-shaped passage to establish a stratified fuel distribution in the passage.