The EVO engines seem to be a mixed bag. I have seen some show up at the field and run great out of the box. I bought the 60 size based on that and am still trying to get it to run properly. I read where the baffel plate in the muffler has small notches that aren't up enough. I removed mine and yes, they were barely open enough to let any exhaust get past. I opened them up but haven't had a chance to try the engine again to see if that solves the problem. Good luck with yours! [8D]