Abstract: A drive unit (1) for a handheld working tool, such as a chain saw, trimmer or hedge trimmer, essentially comprising a housing part (2) with a fuel tank (3) and an engine unit (4) with a fuel supply unit (5) such as a carburetor (5), a muffler (6), and a crankcase scavenged combustion engine (7) with a cylinder (8), piston (15) and crankshaft. The engine (7) has at least one inlet port (9) located in the cylinder wall (10) of the engine and/or an adjacent part of the engine crankcase (11), and the engine's inlet duct (13) from the inlet port (9) up to the fuel supply unit (5) has a length longer than 1.8 times the engine cylinder stroke (18), preferably longer than 2.0 times the cylinder stroke (18).

Abstract: The invention refers to a cylinder (1) for a two-stroke internal combustion engine intended for a handheld working tool, preferably a chain saw, and the exhaust duct (2) and transfer ducts (3, 4) of the cylinder are symmetrically arranged around a mutual symmetry plane (5) which follows the centre line (6) of the cylinder, and at the mouth (7) of the exhaust duct (2) outside the cylinder, a mounting plane (8) with mounting holes (9) for a directly mounted muffler, is arranged.According to the invention, at least one inlet port (11) is located in the cylinder wall (12) and/or in an adjacent crankcase half (10), and the cylinder's in let duct (13) up to the inlet port (11) is so arranged that it forms a fixed and heat-conducting part of the cylinder, and has a length longer than 0.8 times the diameter (14) of the cylinder, preferably longer than 10 times the diameter.