I get some heavy white smoke from time-to-time, but I look at it the way I look at temperature variations, when it comes to a long smoke. As long as the thick white smoke doesn't last a long time, I just shrug it off.
Now, if it didn't go away, then I would worry. But, it always goes away before too long. The wood has to get up to a certain heat, from what I can tell. When it first catches fire, it puts out a lot of smoke, which is just like any other fuel. Once it gets up to optimum temperature, it will burn more efficiently, and as a result, you will get less smoke, and it will be cleaner smoke.
The bigger your wood, the longer it should take to get burning efficiently. I chop my wood chunks up so they get up to temperature quickly. But, a fresh chunk of wood is still going to smoke a bit, and I just let it ride, and it goes away. On a five or ten hour smoke, it just doesn't worry me.
But, that's just me.
CD