a mixture control apparatus for a carburetor which precludes otherwise possible occurrence of fluctuation in the opening angle of the throttle valve even when the engine operation happens to fall near the boundary between the cold state and the hot state . the electric motor for driving the throttle valve is prevented from moving to the side of reverse rotation thereof from the side of normal rotation thereof past a home position after said engine has been changed to its hot state and unless a stop of said engine is detected .