nrok, when you figure this out you're going to love your Lang, I promise.
The fire, is it on a grate or on the floor of the box? You'll want it up a little to allow air underneath.
Was it only wood? I suggest doing a bit of a modified minion method, using charcoal and then once hot put only a split or two of wood on it. This may help especially if the wood isn't 100% as dry as possible.
Also, if you can put the split(s) on the fire warm, that'll help too. I have a warming box on mine and my wood stays up there (one above the bottom, because you CAN have a fire in the warming box; been there DONE THAT).
You'll see below on mine I do this all the time (modified minion method) where I line the box with 3 splits, then charcoal, put lit charcoal on top, and when it gets fully lit I'll put 1 split across the top.
Dont smother the fire either. Too much new/fresh wood or fuel (ala. charcoal) will choke the fire down and produce white smoke as well.
Mine is a very old 84 (called in an 1160 back in the day) and the fire grate was gone, so I built my own. I had this crazy idea of putting it up
just above the air intakes so that the air comes in under the coals. I rather like this now. I do get good clean HOT burns...