I have a Stihl 026 chainsaw which has been working welll for a bunch of years. I went to use it last week and had trouble getting it to run reliably. Once it was running it wouldn't idle and would periodically die even with the throttle open. I opened it up, brushed off the air filter, changed the spark plug, refilled with new gas and still had the same problem. It was usable and I got the work done but the saw was not working properly. During the week I got a new air filter and voila, it is now working the way it should.
I am now cleaning the old filter in soapy water and will test it out, if that doesn't work its going in the garbage and I'm getting a new spare.
So - I have learned that you do need to change the air filter on a chainsaw at least once every 10 years
TTFN