Webby, I had a similar problem with my saw when it was brand new. While cutting wood that was 20+ diam. Saw would start out real good then within a short period of time the chain would just stop and the engine would bog down. What I found happening was wood chips/saw dust clogged up the nose sprocket in the bar. When I took the bar off, the sprocket wouldn't spin or was just hard to move. Once I cleaned the junk out of it I've had no more issues with it stopping the chain.