So I just bought a new Stihl MS 261. I took it out and put about 2 tanks of gas through it. First tank I was cutting small hard maple, 6 inches and less--everything was fine. The second tank, I started working on the bigger part of the same tree, say 12-16 inches. The chain would stop about half way through the cut. The engine kept running. I'd pull the bar out, rev it up and finish the cut. Something worth mentioning is that I had the dealer swap the stock bar/chain for a 3/8 set up (I wanted to be able to swap bars/chains with my other saw). So my questions are these: Did I make a mistake by swapping the bar/chain? Could this just be related to the saw not being broken in yet, or could this be something else? Any guidance woud be appreciated.