I've been around lots of YS engines running castor mixed fuel, and the main problems I have seen are gummed up diaphragms, and more often, stuck exhaust valves from the excessive buildup. I've never used the PowerMaster fuels, but Coolpower Heli 30% is really friendly in the YS
I'm sure Troy will give you a far better explanation of why not to use the castor, but I thought I would share what I have seen.
Chad