Hi Hammerthrower;
Welcome to the forum.
I get a real good bark on my butts, using the Bradley. The formation of bark depends on a lot of factors - salt. herbs & spices, amount of fat, moisture; and the list goes on. If you foil the meat, foiling too early you will not get a bark; even when you foil at the right time, you will get less of a bark. Maybe if you tell us more on how you prepare the meat, the temperature you cook at, if you foil, would be more helpful.