Greg,
Heres a quote from Ron's engine site:- http://modelenginenews.org/faq/index.html#qa5 re castor solubility " Castor oil is not normally soluble in ordinary petroleum oils, but if you polymerize it for several hours at 300 degrees F, the polymerized oil becomes soluble. Hydrogenation achieves somewhat the same effect." So it looks like there is an answer to kero castor only fuel. This also may be why some bottles of castor mix and some dont , depends on how it was processed.
Stewart