PURPOSE: To downsize an engine by simplify the lever pivotally supporting structure of a governor and reducing the space provided for lever operation.

CONSTITUTION: The throttle lever 2 of an air fuel mixing device 1 is elastically pressed to the side K to open a valve by a governor spring 4 through a governor lever 3, and pressed to the side J to close the valve by a rotation detecting actuator 5. The governor spring 4 is spanned to the governor lever 3 and a speed governing lever 6. The middle part 4a of the spring 4 is provided with a high speed setting position regulating lever 7, which can be received by a high speed stopper 8 at a high speed setting position H. The speed governing lever 6 is interlockingly connected to a choke lever 9 through a choke transmission lever 11 and choke transmission link 12 against a valve opening spring 10 so that a valve may be closed. In addition, the choke transmission lever 11 and speed governing lever 6 are swingably supported on the fulcrum shaft 13 of the high speed setting position regulating lever 7.