A guy here has 3 Rotax powered dirt/ street bikes. 2 KTM, 1 ATK.
They look fun as hell.
Adjusting the valves on a air cooled Duc. It's easy. If the motor number is after 751553 it's really easy.
If you like a good story and you like bicycle racing you will enjoy this video.
https://www.amazon.com/ESPN-Films-30-Slaying-Badger/dp/B00MI4WQNU/ref=sr_1_5?ie=UTF8&qid=1483929966&sr=8-5&keywords=greg+lemond
So they sounded great with a tube amp.
Bummer. I don't have a tube amp. My friend had some back in the late 80's.
They were driven by a TOTL Yamaha Receiver. They sounded great but were
fatiguing after a while.