I fly the 20c carb (OEM) and the low setting should be left alone...aside from JUST A TWEAK +/- perhaps an 1/8th of a turn, O.S. does a really stellar job of factory presets. If you are at higher elevations (ie- 2000 ft +) you might need to lean it a bit more, especially running 15%. The trick as a newbie is to eliminate the urge to start twisting and turning everything all at once (assuming someone reading this is). Chase one problem at a time, as pitch curves will often mislead us to start wrenching on the engine. Assuming you have not already done this, try using it at factory settings, first, on the low speed (idle) needle. If you did get a case of the "twisties", call Great Planes Svs Dept and ask what the low end factory setting is, as I forget.

The high speed I have set roughly @ 1.25 turns with 30% on a regular muffler and an enya #3 or #4 (depending on WX or an O.S. #8). My buddy runs this set up with 15% (he's cheap- ), but at roughly 1.12-ish turns out cuz of the 15%.

The only real advantage of 30% is a bit more power and a richer setting, which helps keep the bugger cooler. I like 30%, but 15 % is absolutely fine. However, try to stick to the same fuel once you get some time on the engine. May be a 'Wives Tale' but I still believe in it. I broke in my engine back when I thought 15% was my thing, then went to 30%, which is ok, too, but not the other way around...again, allegedly. Good luck.

keep the skid side up, go mow the grass. -out