PURPOSE: To fully close a secondary throttle valve reliably even when a secondary reset spring is broken, by providing a regulation screw contacting against the secondary rotary lever on a primary rotary lever of a double barrel suction throttle valve open/close system upon reset rotation.

CONSTITUTION: Primary and secondary throttle valves 4, 5 are provided in two suction paths 2, 3 of a double barrel throttle body 1. The valve shaft 4a of the primary throttle valve 4 is provided with a primary rotary lever 6, two torsion springs 7 and angle tension spring 8 while the valve shaft 5a of the secondary throttle valve 5 is provided with a secondary rotary lever 12 and single torsion spring 13. An adjusting screw 22 is provided at the tip of the upper extended section of the primary rotary lever 6. Upon breaking of the secondary reset spring 8, the reset rotation of the primary rotary lever 6 will cause the tip of the regulating screw 22 to forcefully reset the secondary rotary lever 12 through a drive lever 14, and a link lever 16.