Automatic decompression system for starting engine

Claim 1

An automatic decompression system for starting an engine comprising: a cam shaft; a crank shaft; a crank case in which said cam shaft and said crank shaft are disposed; a flange disposed around said cam shaft; a cam formed around said cam shaft, apart from and facing a first side of said flange; a cam gear fitted on said cam shaft so as to contact said flange at a second side opposite said first side; a guide hole expending transversely through said cam shaft between said cam and said flange; a decompression pin provided to pass reciprocably through said guide hole; a fly weight pivotally mounted on a first side of said cam gear facing said cam, said fly weight having an output part for receiving a first end of said decompression pin and a biasing spring means for biasing said decompression pin; and a tappet disposed at a second end of said decompression pin opposite said first end of said decompression pin; wherein said fly weight is positioned between an inner periphery of a rim of said cam gear and an outer periphery of said flange, outward movement of said fly weight being limited by said inner periphery, and inward movement of said fly weight being limited by said outer periphery of said flange; whereby said decompression pin is initially biased upwardly, contacting said tappet, and upon starting of the engine, said cam shaft has a turning speed sufficient to produce a centrifugal force in said fly weight greater than said biasing force, so as to move said fly weight outwardly against said biasing force of said biasing spring means until said fly weight is received by said inner periphery of said rim of said cam gear.