I use Morgan Cool Power Heli fuel, 30% nitro-23% low viscosity synthetic oil, in YS 110, YS 63, Saito 72, OS FS 91II; all idle well, transition to high speed without a hiccup, and run rich and cool. Cool Power Heli Fuel is recommended by Troy Newman for YS engines; he also notes castor oil should be avoided in YS engines as it gums the regulator.

You may wish to visit Troy Newman's website for excellent information and guidance in setting up YS engines. The URL is: http://www.patternflyer.com/troy/?page_id=13

Happy Flying!
Ken