To provide a carburetor for a small engine which can additionally feed fuel for starting and operating a cold engine in an idling condition.

A membrane type carburetor for an internal combustion engine has a low speed passage for starting and idling of the cold engine. An air bleed line of the low speed passage communicates an inlet of a fuel-air mixing passage of the carburetor and a distribution chamber of the low speed passage. The fuel flows from a fuel measurement chamber to the distribution chamber, and is adjusted by a needle screw for low speed idling adjustment. The bleed air and the fuel is mixed in the distribution chamber, and flows out into a mixture passage between a throttle valve and an outlet of the mixture passage. This flow is promoted by the high vacuum formed by the starting and the idling operation of the engine, and further promoted by the substantially closed throttle valve. Since the air bleed line is closed, the fuel-air mixture is thick during cold idling. When the engine is heated, the air bleed line is opened by the valve.