Abstract: A carburetor herein disclosed includes a low speed spray aperture defined on the side wall of an intake duct at a position opposed to a throttle valve inside the intake duct and feeding a fuel for low speed operation in accordance with the degree of opening of the throttle valve, and a by-pass passage having, on the side wall portion of the intake duct, an intake port and a controlling stream spray port whereby the former is defined on the upstream side of the throttle valve and the latter, on the downstream side of the throttle valve. The by-pass passage incorporates therein a controlling nozzle which sprays a jet stream towards the controlling steam spray port. In accordance with an embodiment of the invention, an acceleration nozzle is additionally disposed in the by-pass passage, the nozzle opening into the by-pass passage on the upstream side of the controlling nozzle and spraying an acceleration fuel into the by-pass passage.