This is my 1st time posting on this forum, it's great. I purchased a FS 80 and have run 12 tanks of fuel through it. (Stihl mix and high Octane) The problem is When it's warm and run at full throttle there is a inconsistant popping sound coming from the exhaust. It sound almost like a skip. I brought it back to my dealer and he said it was fine. I doesn't sound fine to me. Any suggestions on how to fix this? Has anyone else run into this problem? I am a home owner and chose to buy a "commercial grade" trimmer so I would not have these problems. Plus the 2 yr warranty is nice. What should I do? Thanks in advance for your replies.