I shall speak in defense of Echos. I Have an Echo Power Pruner, a CS3000 an d a CS3400. They are all super reliable. Paul you live pretty much at sea level, and it is humid -perfect conditions for getting top performance out of the little saw....but even if it were perfectly tuned when you bought it (doubtful) and even if it hasn't been run in enough to require minor adjustment, when you pulled the screen from the exhaust (bless your little thumpin' gizzard) you changed the tune. Follow the Madsen's site instructions-they work(Of course it gets easier with practice)
BTW, First course of action before changing spark plug or adjusting carburetor settings should be a fresh fuel filter.