I maintain my trimmer every fall for winter storage and it start right up and cuts great in spring. Recently I noticed that it starts right up, but once I start trimming the grass it seem to loose power, I pull it away from the grass rev it back up and start again but same problem. I changed filter, plug, and new gas. Starts great, ideals smooth, just no power. I started noticing oil coming out of the muffler, is there something going on with the inside of engine? Any suggestions? Thanks Randy