I was milling this last week and all of the sudden the saw would die when at full throttle or die if it would have any type of load put on it at half throttle. Basically it would start and idle just fine, and even sounded good at half throttle but when I would push to mill it would die, and if I tried to go to full throttle it would die. After it died I never had a problem re-starting it. At first I thought it might be the fuel, but my other saw (same brand) ran just fine with the same fuel, then I thought it might be the fuel filter, cleaned it and even changed it. Also, this happened Wednesday morning, then ran fine after lunch for a while, I didn't mill Thursday, when I went to mill Friday morning the saw ran just fine for a while, until late afternoon, but then it started dieing again so I stopped, started the saw Saturday morning just to see if it would work (not milling) and it worked fine at full throttle. Its almost like something quits working when it gets hot. What might cause this that I am over looking? I am pretty new to saws so it might be something simple, but thought I would ask and see if there are other things to change/try/clean. Thanks *********Answers to other questions I got from anther thread.********* Saw: Stihl 660, 3 yrs old Wood: White Oak, 22" diameter Running before: I used it the weekend before and did not have any issues, ran it through three 8' logs and everything ran fine. Work done: none My FIL and I finally took out and cleaned the spark plug (don't have a new one) and it ran fine after that, but it had been sitting overnight so it was cold, so it probably would of ran fine had we not cleaned it, but I didn't get to mill with the cleaned spark plug.