Preheat the oven to 350 degrees. Grease 12 standard muffin cups and place in the oven to heat. In a skillet, cook the bacon until crisp. Drain on paper towels, crumble, and set aside in a bowl. In a large bowl, stir the flour, cornmeal, baking powder, sugar, and salt together. In a medium bowl, mix the egg, oil, sweet potato, and 1/2 cup buttermilk together. Stir the wet ingredients into the dry ingredients just until blended; the batter should be slightly lumpy. Add another 1 to 2 tablespoons of buttermilk if the dough seems too stiff. Gently fold in the bacon. Spoon into the prepared muffin cups. Bake for about 25 minutes, or until the muffins are browned.