bite the bullet and purchase the quart cans of premix from Stihl, Briggs, Tru-fuel, etc. It's expensive, but we averaged 40-60 dollars to remove and properly ultrasound clean a carb to get things working again. Sta-bil or any of the many other additives don't solve the problem. The tiny carbs have such small passages in them and they corrode when they have water in the fuel.
This, all day. I have a Stihl leaf blower and chainsaw, my dad and uncle both have their chainsaws and weedeaters with leaf blower and pole saw attachments, and my little brother has the 170, which is an awesome saw we've been throwing in the back of trucks anytime we go to the river or camping for what seems like forever, unfortunately we didn't have cell phones with great cameras back then so we didn't take pictures of new toys(we do now). While they are IMO the most reliable out there this junk gasoline we have now wreaks havoc on all small engines, including boat motors.