Abstract: A throttle control system including a throttle valve shaft and a throttle valve mounted at a middle portion with the shaft being rotatably carried on a support and spring-biased in a direction to close the throttle valve, and an operating lever and a control lever connected to said shaft. A first lever is fixed to the throttle shaft, and a lost motion lever is carried on said shaft and is capable of engaging the first lever. The operating lever is capable of engaging the lost motion lever. The relative positions of the first and the lost motion levers are established so that they are engaged with each other when the lost motion lever is rotated in the throttle valve-closing direction and the relative positions of the lost motion lever and the operating lever are established so that they are engaged with each other when the operating lever is rotated in a throttle valve-opening direction.