Re: How to use castor oil??
Don't run it straight. Blending with synthetic oil is fine. Figure out what ratio you want to run over all and then back into it with a small amount of castor.
FOR EXAMPLE: If you decide on 32:1 overall. This is 4 oz to make up the gallon (128 oz) of gas. Use .5 oz castor and 3.5 oz synthetic oil.
I would say whatever blend you decide on, keep the castor less that 1 oz per gallon in your blend or you will foul your plug and build up crud.