One of my Echo PAS-265 (I used mostly as trimmer) was losing it's power and started to run rough at high rpm. - Checked the air filter: oh crap! this thing is covered in oil and dirt (much more than I ever seen one) - Put a new air and gas filter, no dice - checked the spark plug: looked good but replaced it anyway just to try it out, no luck there. - Put some Sea-foam in the gas (usually does wonder for me) but that did not solve the problem and after a few more hours, I really felt the lack of power. The engine is sputtering like crazy at full throttle. - Removed the air filter and ran the engine to see why the air filter was so dirty in the first place and I can see quite a bit of gas spitting out of the cab when at full throttle. - Removed the exhaust and checked the exhaust window by the piston: I can see a small ridge of carbon deposit (about one tenth of an inch) on one side which I remove which a plastic tooth pick (was kind of soft and greasy) - Put back the exhaust: Problem solved, the engine runs like a champ! The little ridge of carbon was creating enough back pressure on the intake to prevent the carb from working properly and make it spit gas/oil mix on the air filter. I run Amsoil Saber at 80:1 instead of 100:1 and that may have contributed to the carbon deposit but I only cleaned it once before (because the manual asked for it) and found almost nothing to clean when I did. Lesson learned: check the exhaust window if the engine seems to lose power or the air filter gets oily. It does not take much for these EPA/CARB engines to lose power because of back pressure in the carb intake. After three years, those PAS-265 are still running strong!