if you have an echo srm 2100 that is a few years old and you are looking to get back some of the power it has lost, you might want to try this. take the exhaust off, put it in a vice. drill the **** out of the inside of it so that it flows better(there are alot of restrictive baffles and turns in there). also take off the piece that is mouted to the exhaust that directs the fumes behind you. the end of it is way to small.if you have tin snips or metal shears you can cut the last inch or so off.put it back on the exhaust. put the exhaust back on the trimmer. and your done. if fired mine back up after doing this and it was running much stronger and not really any louder. i am going to put a new piston and ring in it and it should run better than new. i know some of you would rather just get a new trimmer and that is perfectly o.k. but it seems most of you out there are not afraid to fiddle around with your gear. sorry for the long post, see ya.