Internal combustion engine

An internal combustion engine comprising a combustion chamber having an intake port and an exhaust port, a main intake passage supplying an air-fuel mixture produced by a carburetor to said intake port, an injection port opening to said combustion chamber, an auxiliary intake passage connected to said injection port and supplying air or an air-fuel mixture thereto, a fuel supplement passage for supplementally supplying fuel to said auxiliary intake passage, a solenoid valve for opening and closing at least one of said auxiliary intake passage and fuel supplement passage, an exhaust passage connected to said port, a catalytic converter disposed in said exhaust passage, an oxygen sensor disposed in said exhaust passage either upstream or downstream of said catalytic converter, and a control device responsive to a signal from said oxygen sensor to control opening and closing of said solenoid valve, an amount of air or fuel supplied to said combustion chamber through said auxiliary intake passage being changed by control of opening and closing of said solenoid valve, thereby regulating an overall air-fuel ratio of the air-fuel mixture supplied to said combustion chamber approximately to a stoichiometric air-fuel ratio.