Re: STM valves...
Supreme Tool and Machine makes a set of exhaust valves that are opened by exhaust pressure, and closed under spring tension. Same principle (and some of the same parts) that were used on Rotax engines until 2007. Thet are simple in design and operation, no cables, and you lose a bit of weight. I have a set on my M1000 and on my wife's M8 - would never go back to the OEM system.