Stihl....my opinion, great saws. I have a small one 011, an 028 and an 054 with a 36 inch bar and chain. No complaints and easy to get parts, not that I need many.
finally got around to looking at the saw. I checked the spark arrestor. It has alread been removed. plug looks good. opened up the air filter. the chain oiler tube was in several pieces. airfilter was thoughly soaked in oil blocking off air.
didn't read other responses, but try the gas filter. Pull it and clean/replace it. Do same to air filter. Gas could have gone bad and created a shallack and gummed up the carborator (sp) If that doesn't work, try turning the high idle screw out while the saw is running.
Stihl is a great saw........
I have a Jonsrred 70E, and 2 smaller Sachs-Dahmler (bot great saws as well)
On the running issue when I run into the full throttle lag it is usually the high speed jet. Open it up a hair and try it again. Keep opening a bit at a time til' it does not lag.
This is assuming you have fresh gas, clean filter.
Stihl has two lines of saws as well, they just don't make it obvious. The 026/MS260, 361, 441 are professional saws. The 270, 280, 290, 310, 390, and the Boss equivalents are not. 250 and below (except for the Arborist saws) are labeled for occasional use.