A 20 cc engine isn't small: that's over 1.2 cubic inches. I continue to think it likely that this is an OS .20 (i.e. .2 cubic inches). Is there some reason you won't tell us the approximate size of the engine, from the bottom of the crankcase to the top of the cylinder? That way we would have a good notion of what you have. Saying "it is small" tells us nothing; saying "it is small and it's 20 cc" makes no sense at all.