I have 4 Saitos. I have researched and ask soooo many questions about this oil content thing... but finally came to a decision. First of all....(even if it IS overkill), Saito requires 20% oil content in the fuel. Then it gets sketchy. All I know is that CASTOR will not only gum up the muffler but the internal parts as well.... especially at the valves. I had been running Wildcat Premium Extra 15-18%. The 18% oil is: 20% castor/80% synthetic. I then added 2.5 oz. of synthetic oil to bring it to 20% total oil.
Since talking to many 4 stroke guys.... I have now switched to Wildcat 15% nitro and 18% ALL synthetic oil. BUT....now I add 2.5 oz. of CASTOR to the gallon to again bring the total oil to 20%. There are soooooo many thoughts on this subject, and sooooo many think their mix is correct. I am satisfied with my decision but that doesn't mean it is the only answer. I feel the 20% oil is overkill by Saito. BUT.... I will continue to run 20%.... It makes a coooool smoke trail .....lownslo

PS. I assume that the warrany would also be void with less than 20% oil....if it can be proved???