Internal combustion engine

In an internal combustion spark ignition piston engine having a main combustion chamber and an auxiliary combustion chamber connected by a torch opening, a main carburetor producing a lean mixture, means including a main passage for delivering the lean mixture to the main combustion chamber, an auxiliary carburetor producing a rich mixture, and means including an auxiliary passage for delivering rich mixture to said auxiliary combustion chamber, the improvement comprising, in combination:

• a fixed orifice in said auxiliary carburetor upstream from said auxiliary passage, said orifice being large enough to allow air flow at subsonic velocities when the engine is operated under idle conditions, a fuel compensator system associated with the auxiliary carburetor and operating to control the air-fuel ratio of the mixture produced therein, and sensor means responsive to engine operating conditions for causing the compensator system to vary the concentration of the mixture produced by that carburetor, said auxiliary carburetor upstream from said auxiliary passage having no movable throttle valve, a movable throttle valve in said main carburetor upstream from said main passage, whereby said fixed orifice serves to control the amount of rich mixture delivered to the auxiliary chamber when the main throttle valve is opened to cause the engine to operate at a speed greater than idle speed.