A Honda GCV 160 will run perfectly fine on just about any oil. I have one of these engines, and I've used SAE 30, 10w-30 conventional, 5w-30 synthetic, 5w-40 synthetic, and 10w-30 racing synthetic. I haven't noticed the slightest bit of difference in performance or consumption (it has ZERO measurable consumption) with any of these oils. I always just use whatever oil I have hanging around when I'm changing it.