Enya 40SS has a iron piston, it's not an ABC engine. Not having a ring sometimes get people thinking is't ABC, but it's not.
Cast iron piston requires break-in more like a ringed engine.
Run it rich, almost 2 cycling in a series of shorts runs ( 1minute), then leting it cool down between runs. Then progressively increase run time (2 min, 3 min, 4 min) and then start running it less rich.
Takes more time to break in than an ABC but if done properly the piston/sleeve fit will be very good.
Enys engines are known to take more time to break in, but if you do it rigth, it will last a loooong time. I have one, very reliable engine. 5 years of use and it's running like new.