Abstract: A decompressing device for facilitating starting of internal combustion engines, by lifting one of the engine valves at the beginning of the compression cycle, comprises a lever which is movable, by hydraulic pressure developed by an engine-driven oil pump, from an extended position in which one end of the lever effects said valve lifting to a retracted position. Lifting of the valve therefore stops when the engine speed (and hence the hydraulic pressure) reaches a predetermined level. The lever is moved between the extended and retracted positions by piston means located in a bore in the engine camshaft, the piston means being acted upon in one direction by the hydraulic pressure, and in the opposite direction by resilient means which tends to move the lever to the extended position.