I'm not sure about this i used to run RC planes and we would Castor oil...using it in this way first get 93 gas remove the alcohol get some 2 cycle oil the 93 will come out to about 89 oc 35:1 3.66 oz per gal or 109 ml per gal seeing you ask about castor oil from what i can remember does not burn off that much for a gal of gas all you need is 0.10 oz or 2.8 ml unless you are going to run nitro fuel you are on your own but at 50.00 a gal...I know some of the people is going to disagree at 70 years of age that gas and oils mix with castor oil is what my friend in AZ. run in his Moped all the time...