Only thing I can think of is the wood is catching fire instead of smoldering. I've had that happen to me a couple of times and now that I think about it, it did sort of have a burnt taste to it. Try putting the wood in a different part of the fire box and see what happens.
Your problem is definitely the exception and not the rule. I just finished smoking a 5.5lb. bird for dinner in my 020. Some garlic powder & Canadian seasoning, 1.2oz. chunk of orange wood. Smoked for about 1 1/2 hrs at 250. Then finished up in a 400 degree oven to crisp up the skin. Juicy, nice smoke flavor and nice crisp skin.