Thanks for the update. Are you seeing the "belch" as well? This usually happens in the first heating cycle and is preceded by dark thick smoke and puffs of smoke where the smoke stops, then starts, then stops a few times. Following this, I get the "belch"--a massive exhaust of steam/smoke and then the smoke looks fine. If you are seeing all of this, then your wood is likely dry. Dry wood tends to combust, while wood chunks with higher moisture content can push through the initial heating cycle without the "belch".
I should note, however, that I always get a thicker smoke in the first heating cycle, regardless of whether I experience the "belch". This usually happens around 180* on the first cycle, and then the smoke tapers back down when I get past 200-210*. After the first heating cycle, I don't really get heavy smoke - it tends to taper off to a nice steady light smoke.