Automatic decompression device

An automatic decompression device of a small OHC engine in which a decompression lifter provided inwardly of an exhaust cam face of a cam shaft in a radial direction of the cam shaft such that the decompression lifter is outwardly protrusive or inwardly retractable in the radial direction from the cam face, by rotational operation of an operating shaft inserted concentrically with the cam shaft in the cam shaft, is protruded by a decompression control mechanism when the number of revolutions of the cam shaft is below a predetermined number of revolutions, for reducing a pressure in a cylinder when the engine is starting, wherein

• the decompression control mechanism comprises:
• a pair of weight members provided at an end portion of the cam shaft, the weight members each including a pivot portion pivotably attached to the cam shaft at a position apart from a center axis of the cam shaft such that pivot portions of the weight members are provided to be symmetric with respect to the center axis and a tip end portion engaging with the operating shaft and extending toward an opposite side of the pivot portion of the weight member with respect to the center axis;
• and
• a bias member for biasing each of the weight members in a swing area of the weight members.