Fuel for idle operation is supplied through the main jet to a well directly below the main discharge jet. The idle passage connected to this well is restricted by a small drilled hole near the bottom of the passage. The fuel travels up this channel and through the idle jet calibration to be mixed with air originating back of the main venturi. The amount of air admitted is controlled by the idle adjusting needle. The position of the needle in this passage controls the suction on the idle jet and, thereby on the idle fuel-air mixture. Turning the idle needle IN (clockwise) increases the suction on the idle jet for a richer mixture. Turning the idle needle OUT (counter-clockwise) increases the amount of air admitted to reduce the suction and deliver a leaner mixture. Fuel and air are mixed in the passage leading to the discharge port (priming plug) before entering the air stream.