Speed was controlled by means of a throttle valve lever. Continuous valve lift systems typically allow for the elimination of the throttle valve. The N360/N600 controlled gear changes by balancing a throttle valve and a centrifugal valve. On 20 September, the port engine stopped after a throttle valve broke down. The relay piston moves upwards and the throttle valve spindle ascend upwards opening the valve. The inlet had a secondary throttle valve sandwiched underneath the primary throttle body. Late models, from the 134, used a Corliss throttle valve instead to avoid this problem. The further the pedal is pushed, the wider the throttle valve opens. Ideally, the throttle valve remains open as much as possible to avoid throttling losses. A throttle valve, connected to altitude and ram pressure instruments, controlled fuel flow.