Sthil FS80, starts perfect, idles fine, runs wide open great for about 5 mims. then no power. Plug gap is perfect, the ceracic is a light brown, tan color, spark screen is clean. Running 50:1 gas. At the time it starts losing power I believe it is getting hotter than usual. I use to be able to run this thing for 3-4 hours wide open with no problem. Any suggestions please let me know.