Internal combustion engine provided with decompressing mechanism

An internal combustion engine comprising:

• a crankshaft;
• a camshaft driven for rotation in synchronism with the crankshaft;
• a valve-operating cam formed on the camshaft;
• engine valves operated for opening and closing by the valve-operating cam;
• and a decompressing means for opening the engine valve in a compression stroke in a starting phase;
• wherein the decompressing means comprises a flyweight supported for swing motion by a pin on the camshaft, a decompression cam that operates together with the flyweight to exert a valve-opening force on the engine valve, and an arm connecting the flyweight and the decompression cam, the flyweight has a weight body and projections projecting from the weight body and engaged with the pin, the pin is disposed such that an axis of swing motion of the flyweight is included in a plane substantially perpendicular to an axis of rotation of the camshaft, the weight body is a block of a width along the axis of swing motion and a thickness along a radial direction which are greater than a thickness along the axis of swing motion of the arm, and the weight body overlaps the camshaft as viewed from a direction perpendicular to a reference plane including the axis of rotation of the camshaft and parallel to the axis of swing motion.