Most newer saws have plastic caps to prevent people from adjusting mixture screws too far. Stihl took that one step further and eliminated the high-end adjustment screw on the 020T (another reason I dislike the saw).
If you have an older saw without caps, most of them start at 1 1/2 turns out from seated. Bigger Stihls are 1 turn out. If the saw idles but seems to run out of gas when you pull the throttle, your high-end jet may be clogged. Likewise, if it runs full speed but won't idle, or stalls when you try to rev it up- your low end jet may be clogged.
If all else fails, replacement carbs are about $50-60 at the dealer for that size saw generally. About what 2 hours labor costs.
As for 2-cycle oil, your best bet is to use the manufacturer's branded oil and mix according to the directions. 2nd alternative is Husky or Stihl 2-cycle mix, following directions on the bottle.
