I've read here from someone who did that succesfully, but haven't tryed it myself...

I run always castor oil.... und despite the mess, I think I still like it more...

I have a 4 stroke engine, yesterday at the field was pretty warm, and I changed from a fuel with castor to a fuel with synthetic to make a test....as soon as the fuel with castor was used (in the line I think)...the engine dropped about 300 RPM....and I think that the fuel with synthetic wasn't so good at high temps outside, the one with castor worked as usual. The last weekend I used the same fuel with synthetic, and it worked well, I couldn't tell the difference between the two...but it wasn't so warm... I don't intend to start again (128319273981273 times here) a discussion about the castor/synthetic oils....but it seems to me that in all the cases, that castor will help to seal better.

Saludos,

Jorge