I have an Aviastar .46 and it's a great engine, BUT..... it was hell breaking in. I had to get all the air leaks sealed up as well.
Some folks say you don't have to do that, but I couldn't get this thing to transition at ALL, even after I sent the carb back to Sig. After I put red RTV silicone around the head, back plate and the throat of the carb, it ran MUCH better, but it'd still load up at idle and die eventually. So I put it on a SPAD FNS and ran it wide open the entire time. Man, that thing is a SCREAMER!
Once I finally got it broken in good, it transitions pretty well now. It's hard to go wrong with this engine at 49 bucks, but I sure wouldn't recommend it for a beginner. I was pretty green when I got mine and I was pulling my hair out.