A torsion spring that is used in a throttle valve device increasing and decreasing an opening degree of an intake passage or an exhaust passage of an internal-combustion engine includes: two coil springs connected with each other so that torsion directions are opposite from each other; and a hook disposed between the two coil springs. Of the two coil springs, one side spring arranged at one side in an axial direction biases a valve object to a closing side, and the other side spring arranged at the other side in the axial direction biases the valve object to an opening side. In at least one coil spring of the two coil springs, a dimension of a clearance between the at least one coil spring and the hook connected with each other is larger than an average value of clearances between coil turns of the at least one coil spring.

An exhaust valve includes a body defining a passage and a flap that pivots about an axis relative to the body to selectively close/open the passage. An actuator moves the flap and a device couples the flap to the actuator. This coupling device comprises: a compression spring having a proximal end that rotates about the axis with a first element between the flap and an actuator output shaft and a distal end; a seat engaged with the distal end, while the seat is fixed in rotation about the axis with the first element, and a torsionally-rigid transmission member fixed in rotation about the axis with the first element and that immobilizes the distal end relative to the proximal end in a plane that is orthogonal to the axis. The transmission member has a slot that is elongated parallel to the axis and is traversed by the distal end.

A torsion spring that is used in a throttle valve device increasing and decreasing an opening degree of an intake passage or an exhaust passage of an internal-combustion engine includes: two coil springs connected with each other so that torsion directions are opposite from each other; and a hook disposed between the two coil springs. Of the two coil springs, one side spring arranged at one side in an axial direction biases a valve object to a closing side, and the other side spring arranged at the other side in the axial direction biases the valve object to an opening side. In at least one coil spring of the two coil springs, a dimension of a clearance between the at least one coil spring and the hook connected with each other is larger than an average value of clearances between coil turns of the at least one coil spring.

An internal combustion engine kart implementing an accelerator cable connecting an accelerator pedal and an operating lever rotating an air inlet flap controlling the amount of air entering the engine, and a controller receiving at least one control signal emitted by a remote transmitter. The kart includes a movable stop acting on the operating lever so as to change its range of movement and consequently a level of maximum opening of the air inlet flap. The movement of the movable stop depends on the control signal.

A throttle valve assembly includes a valve housing having a main channel and an auxiliary channel. A main throttle valve is pivotally mounted in the main channel, and an auxiliary throttle valve pivotally is mounted in the auxiliary channel. A common rotating actuator controls the opening angle of both the main throttle valve and the auxiliary throttle valve through an actuating mechanism. The actuating mechanism includes a crank mechanism connected between an auxiliary pivoting shaft and a gear train driven by the rotating actuator.