An apparatus for atomizing liquid fuel while mixing it with air, and varying the amount of each while maintaining a substantially constant fuel/air ratio for the intake manifold of an engine. The apparatus includes a frame (16) forming a passage (14) with a throat (44), with a second wall (56) of the passage being moveable toward and away from a stationary first wall (54) of the passage to vary the cross-section of the passage and thereby vary airflow. A fuel-carrying tube (24) has a proximal end (60) fixed to the first stationary wall and has a distal portion (62) that extends through a bore (64) in the moveable wall and with the moveable wall being slideable around the tube. The tube has at least one aperture (70) for flowing fuel into the passage, with the exposed aperture area being progressively increased as the moveable wall moves away from the stationary wall to flow a progressively increasing amount of fuel into the passage. The moveable wall is moved by a lever (134) that can be moved by the throttle of the engine.