Two issues you need to consider for oil selection is the high operating temperature of an air cooled engine and compatibility with the wet clutch. Castrol
10W -40 is a car oil and I would not run it in any air cooled motor because it doesn't have the high temp stability of some other oils, and it is not JASO-MA certified for wet clutches.
I have not had good luck with Honda
branded oils, and Honda doesn't publish oil specs like all of the major oil providers do so I class their oils as snake oil, and their performance in my XR200s support that.
The best cheap oil you can use in your air cooled engines is Shell Rotella T purchased at Walmart, next best is Rotella T6, a synthetic with better high temp stability but a higher price. Both are JASO MA rated for wet clutches. I've tried other race oils and synthetics in my PowRoll 218cc engine and I'm back to Rotella T6. The published specs support my decision.