| 摘要 |
PURPOSE:To aim at increasing of engine braking force by installing a flap plate in an exhaust port, and setting an upper end of the exhaust port to a lower position at time of deceleration. CONSTITUTION:A flap plate 8 is installed in an upper edge of an exhaust port 4, driving this flap plate 8, and it is moved up and down at an upper end position of the exhaust port 4. A turning position of a throttle grip 31 is detected by a throttle sensor 32, and at time of deceleration, the flap plate 8 is turned round and the upper end position of the exhaust port 4 should be set to the lower position. By this constitution, full-close timing of the exhaust port is quickened so that engine braking force is increasable.
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