I've seen 3 guys at my field who had the YS.

one had it in his Jekyll and finally gave up and sent the YS back to get rebuilt and relooked at by YS.
The other Just couldn't get it running right and had to adjust valves and still could not get it running.

The third guy too his out, put it in the back of his pick up truck and replaced it with a OS1.20 4stroke. And everytime he comes to the field, he has the YS in his truck bed still, with the prop on it. he's an experienced veteran pilot but refuses to mess with the YS.

So out of the 3 YS i have seen, none have worked correctly.

All 3 pilots have said that the YS produces more power than their equivalent competitors, but what's the power mean when they can't even get it running half the time.

So with YS track history and your experience, I'd say stay away from YS for now.