I use 15% "Cool Power" in all of my engines, (OS 2 strokes OS 4 strokes and a YS 4 stroke) and it runs all of them beautifully.

Interesting. Cool Power is 17% pure synthetic. I know that os says 18% plus for all engines and specifies some castor for the ABN 2 strokes. And I believe YS reccomends 20% oil.

You've never had any trouble with 17% oil? Wow.