Abstract: A power unit comprises an internal combustion engine adapted for operating with natural induction, supercharged by a turbine-compressor unit receiving the exhaust gases of the engine. The compressor supplies air to the engine through an intake pipe provided with an atmospheric air inlet closed by a check valve in operation under load. The power of the engine is controlled by a power control member movable by an operator between a maximum power position and an idling position. An inlet valve, placed in the air inlet of the compressor and movable between an open position and a closed position, is biased towards closure by the power control member when the latter is moved towards its idling position. A locking member responsive to air pressure at the outlet of the compressor cooperates with said inlet valve to prevent its closing as long as the air pressure at the outlet of the compressor is greater than a predetermined threshold.