YS recommends 20% nitro and 20% oil in all of it's 4 stroke engines. Many of the top fuel manufacturers sell this blend known as YS 20/20. In warmer weather some of the YS engines will do ok on less nitro. Our recommendation is to go easy on any castor oil in the fuel. A couple of percent is OK, but any more is asking for regulator problems. Those of you with corporate funding may want to try 30% Helicopter fuel. Hard on the wallet, but very addictive!!!!