Abstract: A two-stroke engine is disclosed which is controlled by a carburetor throttle valve and has a crankcase subjected to continuously alternating overpressure and underpressure. A pneumatic control member responsive to a signal dependent on the rotational speed of the engine is in pressure communication with the inner chamber of the crankcase via a valve. The output member of the pneumatic control member is connected with the throttle flap of the carburetor. The valve provided between the crankcase and the pneumatic control member is responsive to a signal for controlling the pressure in the pneumatic control member. This valve can be configured as a resonance control valve fixedly mounted to the housing of the engine.