Thanks for the link-I will check more into that. From what I just found on an online Echo manual, its states that the SRM 1501 is in fact a 21.2cc engine. I guess I will have to tear it down and see what everything looks like. Hopefully, I can find my way through this as I don't have access to a lathe and so on. I will try and post a couple of pics when I get a basic strip down.