P 4 of the manual - see "after starting fire": http://www.keystoker.com/manuals/2012/K ... -Stack.pdf
My printed manual is a few years old, and worded a bit differently, but it states that "there is no substitute for a draft gauge in making these adjustments" I will admit that I frequently dink with the feed, and air, and baro setting. I guess it's a matter of opinion, or technique as far as air adjustment. The only opinion that I've read here more than once and find a bit silly [ok, flat wrong] is that the air " shutter" should NEVER be touched, and remain at the factory starting point of 1/2 open. It's a starting point.
That said, obviously, you don't want to shove still burning coal into the bucket [too little air, or too much feed?]. Someone here recently wrote that the ideal setting is when the coal is completely burned just before it reaches the last air holes on the grate while the unit is running flat out. Then again, if one [or me LOL] blows an excessive amount of air through the grate in the quest for no unburned pieces in the bucket, are they [or I] are blowing heat up the flue and wasting money just to have nicer looking ash in the bucket? Someone else stated that they don't mind some unburned chips in the bucket, and would rather have that than blow more heat up the flue.
Who is right? I wish that I knew.
p.s. - fwiw, imo, the coal used will effect the best setting of the air shutter. I bet that if one would screen all the fines out of the coal, much less air would be needed. Coal with lots of fines, or typical undersized rice [more like barley] tends to need more air to burn well. At least from what I see.