In a large skillet, fry the bacon until crisp, then remove it and set aside.  Drain all but 2-3 tbsp of bacon drippings.  Cook onion in drippings until tender.  Stir in flour and blend well.  Add vinegar and water.  Cook and stir until bubbly and slightly thick.  Add sugar and stir until it dissolves.  Crumble bacon. Gently stir in bacon and  the cooked, sliced potatoes.  Heat through, stirring gently, to coat the potato slices. Serve warm.