Big, I still have an OPS .60 with the slide carb, that's a fun one. I have a nice old ST .40 from Italy, the MECOA .46, several HP .25s and I think four MDS engines. One of the MDS .68s ran pretty well, the other one didn't and I went through three of the .58s and never got one to break in before the engine broke. The castings!! I still have one of the .58s in the box, I have three flights on it. Russia saw fit to try to get back at the U.S.A. with those.
There is nothing about the SK that is hard to tune, the break in is just different and must be done before flight. OS I just fire them up and go then break them in while in the air.
I like the SKs better then the OS engines so that's saying a lot, I really like the OS engines in two strokes. I was the pit man for a race pilot that used nothing but the Webras, another easy engine and I like them, we kept getting beat by a pilot using the Fox!! But the Fox was a Lee built engine!!
There are a lot of good engines out there, some are just better then others!!