Abstract: An improved idling system for a carburetor in which the idling fuel is directed into the carburetor or manifold at a point spaced downstream from the throttle valve, and an air bleed modulation passageway for conducting air to a position adjacent the outlet of the idling fuel for controlling the air pressure at the idling fuel outlet for controlling the idle fuel flow rate. The air modulation passageway varying the idle fuel delivery as a function of throttle position and manifold pressure. A vortex chamber having a tangential air inlet for receiving and atomizing the idle fuel and air. Various tail pipe modifications may be connected to the outlet of the vortex for varying the fuel delivery characteristics. A convergent-divergent passageway may be provided between the idle fuel-air mixture prior to its injection into the intake manifold. Hot exhaust gases may be injected into the idle fuel-air mixture for better atomization, and exhaust gas may be used to externally heat the air-gas mixture.