Crankcase scavenged internal combustion engine (1) of two-stroke type, intended for a working tool, preferably a chain saw or a trimmer, and provided with a light-weight and compact muffler (2). The engine is arranged with a particularly high crankcase compression created in that at least one filling (3, 4, 5, 6) is placed into the compression area (7) under the engine piston (8) in form of a filled balance (3) and/or a piston filling (4) and/or a piston washer (5) and/or a stationary filling (6), at the same time as the engine is provided with an especially strong throttling created in the engine's exhaust side, i.e. in its exhaust port (9) and/or in a possible exhaust duct (10) and/or in the muffler (2).