bemyself,

Model airplane fuel is composed of three ingredients; methanol, nitomethane, and lubricant. The lubricant component is usually a mix of synthetic and castor. In my case I use a blend of 12 1/2 % nitro and 20% lubricant ( 18% synthetic and 2% castor). The castor will help in preventing excessive heat, but tends to leave varnish deposits on the engine, hence the small castor percentage.

The nitro - lubricant percentages are not directly related. In other words, the nitro content is separate from the lubricant. The nitro content can be 5%, 10%, 15% or even 20%, or anything in between, but the lubricant would be constant at 20%. If I understood your post, it seems to me your "home brew" had way too much castor.

That's my understanding of fuel. Hopefully someone with more knowledge on the subject will add a post.

DaveB