Castor oil IMHO is cheap insurance. Caster oil will protect an engine in a lean run condition. I would never fly without some in my fuel. I run 20% oil in my engines. I also like 3-5% castor. I know the goop is a pain but I live with it.

As for castor in a 4 stoker. I am looking at the manual for a Saito 80 right now. It said "any castor oil based fuel or synthetic system fuel on the market, high quality glow fuel(containing about 20% oil) in the 5-15% nitromethane range is recommended." I personally run 10% nitro and 20%oil with a castor mix (Byron's 10% sport mix) and have no problems with my Saito's. A change in glow plugs may be necessary. I had to change the one in my 50 to make it work ok. Used a Fox Miricle plug. Works good.

Mark Shuman