Are you choking it when cold engine? I've used gas additives like "Seafoam" in both 2&4 stroke engines to help clean out fuel tanks that sit in out buildings over the winter. My saws, mowers, tractors & motorcycles have all liked the "Drygas" type additives as well as Stabil. Before Stabil I had a lot of fuel cleanout work.
Checkout the guy who has a Youtube shop, explains everything with video. He drinks a beer and is entertaining. Someone here knows the guy. I think he's from Canada and has a Stihl banner.