cjm3, I too have just started my 520 last sunday (love it). Currently running it on 3 teeth. I tried from 3 to 3 1/2 on air setting an what do ya know, ends up 3 1/4 is best setting, just where EFM says to put it.
I dont want to imply that you are not mechanicaly inclined because this step is not as easy as it seems, the step of counting the auger teeth. Are you sure that you are at three teeth and not 2 teeth? I know I would goof this up if it werent for stoker scot showing me a trick. You run the stoker for a second or two then kill the power. when it slowes down enough it is easer to count those little clicks. It just seems that you are not getting enough coal and it is burning inside the pot too far in my nieve opinion. I dont question the air because that is cut and dry simple. What brand coal are you using? I am using Blashac with good results. Hope you dont take offence with my implication of a simple mistake.