A carburetor for feeding separate lean and rich channels of an engine intake duct includes a body having a mixing passage with an air intake side and an engine outlet side. A throttle shutter is rotatable about an axis transverse the mixing passage, and a partition is located within the mixing passage upstream of the throttle shutter. The downstream edge of the partition is adjacent the throttle shutter axis whereby in use of the carburetor the partition defines an extension of the lean and rich channels upstream of the throttle shutter, the partition thus providing substantial isolation between the lean and rich channels for all rotational positions of the throttle shutter. In a preferred embodiment a choke shutter is located upstream of the throttle shutter and is rotatable about a further axis transverse the mixing passage, the upstream edge of the partition being adjacent to the axis of the choke shutter.