US Patent 7140340 Decompression device for engine

A return spring is constituted of a torsion spring, a spring part is held at a position different from that of a shaft part of a flyweight, and a free end portion of the return spring is hooked to a slide unit of the flyweight. The position of transmission of an urging force to be transmitted from the return spring to the flyweight is different between an angle-closing side and an extending and opening side. By tuning the shape of the slide unit, the position of protrusion of a spring fixing pivot, or the like, the distance from the shaft part to a contact point of the free end portion when the flyweight is located at the angle-closing position is set to be larger than the distance from the shaft part to the contact point of the free end portion when the flyweight is located at the extending and opening position.