YS engines love high oil, namely 20%. They also like higher nitro amounts than most other 4-strokes. I like 20% to 25% nitro in YS 4-strokes.
Don't be afraid to run a fuel with just a touch of castor in it. Through hundreds of gallons of running YS 4-stroke test engines, I found that 18% synthetic and 2% castor will not gum anything up in the regulator or coke up the valves. Any more than 2% castor over an extended period of time, the valves will start building up deposits and the regulator gets gummy if they sit for long periods.
All synthetic is fine too as long as you run it at 20% by volume.

In addition to the Wildcat and Powermaster, Cooper's and S&W fuels are also compliant with YS warranty requirements.


Fuelman