I use Byron's 15% castor / synthetic blend and all my engines run great.
So I use this on a variety of glow engines, 2 stroke form .15 to .90 and my four strokes form .70 to 1.20. and a helicopter as well.

There are a lot of discussions, about brands and mixtures. I have not had any engine problems, and if I take one apart, there is almost no deposit to find. Everything is tight and no wear to see. So I guess I'll stick with it.