My experience is good in buying used engines, I bought ASP .46 it was the best engine, almost new just needle valve was broken, infact that engine I bought it from the scrap, so me and my friend goto junkyard and guys over there save those engines for us, so that we can buy them. I bought HB .61 engine, it did give me hard time specially the carburetor but engine's running, rpm's and compression are excellent. But what I have learned from the experience of mine ofcourse it's a short experience that better buy new engine, at least you don't have to worry for coming years specially when engine runs to the best.

Mody