Amusing all this. I have a smattering of 2-stroke brands here, and they all get the same gas/oil. Super (no ethanol) gas and 45:1 Castrol 2T oil. I use that stuff, because it is available for cheap at auto parts stores, comes in quarts, and it is rated FB. Even Echo only has FC rated oil now... along with a lot of others. I no longer use Stihl or Husky oil, 'cause they do not certify them to any standard. So there is no knowing what's in there.
I also add gas stabilizer, but we use all these tools so often there is no reason to. I have a Homelite blower that I bought 20 years ago and stored (empty; light oil coating in the cylinder) for 15 years, and after all that time it fired right up. The Stihl FS85 weedeater tends to sit for months, and runs fine on old or new stabilized gas. The Echo chainsaw is the same. That thing should have died 4 years ago. But it is still going.
All this being said, this looks like a straight gas issue. We have a 290 that is the little brother to the 310. It gets abused, and Stihl runs like a top. I have bought many a 2-stroke engine part on EBay that were scored. You should see the motor on the 250 I just got. Deeply etched... I will have to post some pix here. O/w it is a $300 near new saw. The seller admitted it was straight gas in the tank. Too easy to mess up mixing gas, and kids and wives mess things up. I have 2 one gallon containers here that are the ONLY ones that are used to fill all the 2-smokes with. I mix them myself. We have like 5 types of gas here on the farm.
Hey, maybe he ran it on diesel?