I have a ECHO straight shaftweed whacker that I bought new in 1983. I run it about an hour each week during the mowing season. Almost all of the time it is running at full throttle. I use OPTI II oil, and have since it was new (Optimall was what is was called when new). I'm on carb kit #3 and spark plug #2. 0.020 gap seems to work for me.

Joe