Cook the bacon over moderate heat until crisp. Drain and pat dry. Reserve 2 tablespoons of bacon grease. In the reserved grease, sautee onion and the celery until the onion is softened. Add the sugar, the flour, and the celery seeds, and cook the mixture, stirring, for 30 seconds. Stir in the mustard, the vinegar, and 1/2 cup water, bring the mixture to a boil, stirring, and simmer it for 2 minutes, or until it is thickened. Pour this dressing over the potatoes. Add in eggs, pickles, and crumbled bacon. Serve the salad warm or room temperature.