Abstract: A portable, internal combustion-engined tool includes a combustion chamber (1), a piston (8) adjoining the combustion chamber (1), with a pressure build-up in the combustion chamber (1) providing for movement of the piston (8) from its initial position, in which the piston adjoins the combustion chamber (1), away from the combustion chamber (1). A brake device (43) retains the piston (8) substantially in its initial position during build-up of pressure in the combustion chamber (1), with a braking force applied to piston (8) being changeable for adjusting the amount of energy generated in the combustion chamber and transmittable to the piston (8).