I've tried almost all brands of trimmers and it seems after awhile they begin bogging down and loosing power. I would remove the spark arrestors and that would help for awhile but eventually they would just quit working. One day I took the muffler off and was inspecting the carbon buildup to see what else I could do to get the power back up. I happened to look at the exhaust port on the engine where I had just unbolted the muffler. I took and flashlight and shined it in there. I couldn't believe it. It was almost completely sealed of with carbon buildup. I made sure the piston was up all the way and took a tiny flat screw drive and began scraping it out. I used parts cleaner to flush it clean when I was done. I put back on the muffler and wham the thing fired up just like new. It had power and everything. I began digging in my trimmer "bone yard" and found 2 echos that I thought were dead. I did the same thing and now they are both running again. I can't believe that I have thrown away probably 4 trimmers and blower because the dealer couldn't even figure it out. Anyway just thought I'd share my experience in case your suffering from the trimmer bogging down and loss of power. Take your muffler off and look in there. You might be surprised.