A crankcase scavenged internal combustion engine of two-stroke type (1) having at least one cylinder (15) and at least one air passage arranged between an air inlet (2) and the upper part of a number of scavenging ducts (3, 3') with exhaust orientated scavenging ports (9, 9') located close to the exhaust port (19) of the cylinder. At least one intake orientated scavenging port (14, 14') is located close to the inlet port (33) of the cylinder and is fed by at least one scavenging duct (5, 5'), and the air passage and the scavenging ducts are so arranged that the scavenging ducts (3, 3') can be supplied with and hold so much air that they during the following scavenging process will scavenge essentially nothing but air. The air passage is arranged from an air inlet (2) provided with a restriction valve (4) controlled by at least one engine parameter, e.g. the carburettor throttle control, and the intake orientated scavenging port/s (14, 14') is/are so arranged that it/they begin/s to scavenge the air/fuel-mixture (2) later than the scavenging ports (9, 9') begin to scavenge air.