Patent ID: 8746192

Claim:
A scavenging method for use with a two-stroke internal combustion engine having a scavenging passage in communication with a crankcase and a combustion chamber, comprising: introducing air into the combustion chamber in a first portion of a scavenging stroke; introducing lean air-fuel mixture in an amount regulated at least by a crank angle in a second portion of the scavenging stroke, which is subsequent to said first portion; and introducing rich air-fuel mixture of a predetermined air-fuel ratio in a third portion of the scavenging stroke, which is subsequent to said second portion, wherein the scavenging passage is sequentially supplied with air, lean air-fuel mixture and rich air-fuel mixture in this order through an end portion of an exit end thereof from a carburetor by opening and closing of an air port and a mixture port with a stroke of a piston regulated by crank angles, said lean air-fuel mixture being prepared by concurrently opening the air port and a mixture port and diluting air-fuel mixture supplied through the mixture port with air concurrently supplied through the air port, and wherein, in each scavenging stroke, the combustion chamber is supplied, from the exit end of the scavenging passage, first with said air, next with said lean air-fuel mixture, and next with said rich air-fuel mixture.