Internal combustion engine provided with decompressing means

A decompressing mechanism (D) included in an internal combustion engine comprises a flyweight (81) supported for swing motion by a pin (71) on the camshaft (15) of the internal combustion engine, a decompression cam (82) and an arm (83) connecting the flyweight (81) and the decompression cam (82) and having the shape of a plate. The flyweight (81) has a weight body (81c) and projections (81a, 81b) projecting from the weight body (81c) and engaged with a pin (71). The weight body (81c) is a block of a width along the axis (L2) of swing motion and a thickness (t2), along a radial direction, which are greater than the thickness (t1), along the axis (L2), of swing motion of the arm (83). The weight body (81c) overlaps the camshaft (15) as viewed from a direction perpendicular to a reference plane (P3). The decompressing means (D) is small, lightweight and is capable of concentrating most part of its mass on the flyweight (81).