Abstract: A four-cycle reciprocating-piston internal combustion engine having a main combustion chamber connected by a spill port with an unflushed ignition chamber. A fuel injection nozzle and a spark plug are arranged at the ignition chamber at angles with respect to one another. Fuel supply means are also provided at the main combustion chamber for supplying a substantial majority of the fuel consumed by the engine during operation. In order to maximize the effectiveness of the ignition chamber, while minimizing the high peak pressures, the ignition chamber and spill port are constructed so as to have an extensive homogenization of the fuel proportion injected into the ignition chamber. In preferred embodiments, the ratio of the volume of the ignition chamber to the total compression volume of the engine is in the range of 0.10 to 0.30 and the ratio of the volume of the spill port to the total compression volume is in the range of 0.01 to 0.25.