ORIGINAL: paladin
I also had a YS 90 but I've seen alot of people with truble with those engines lately and I think you all would like to here how it flys not about engine troubles, and the 1.2 is a known commodity.
I would use a YS 110 or an RCV 120-SP in this plane. I don't see any YS engine troubles in the engines forum. I don't know about the YS 90, but all five of my YS 110's run like clocks.
The problem is that this plane has a slender chin, so an OS 120 four stroke would stick out too much