The YS needs 20% oil and the more nitro the easier it will be to set. Most fuel manufacturers make a YS 20/20 blend. There are some that will tell you to use all synthetic and stay away from castor but a little castor won't hurt. The biggest pain with fuels that contain castor is they tend to clog up the regulator if you let them sit without running them completely dry.

The basic 4 stroke fuels are normally lower oil content than 2 stroke blends which is why you will see YS cautioning against it.