Homelite chain saw: loss of power?

I can get the chain saw to full high speed without a load on it. As soon as I begin to cut a piece of wood the chain saw begins to lug down and loses power. I have tried adjusting the high speed needle valve; checked the chain to make sure it's not too tight; checked the fuel mixture but to no avail. I also took the filter off and and the muffler off in case there was any restictions of either. Can you give me ideas to check further?

Make and model is not known at this time;this is a general question. THe chain saw IS old and has cut many trees.

Could it just be worn out?

Richie L.
September 2007