Boil 6 potatoes in their jackets. Peel and slice them thinly while they are hot. Saute 1/4 pound bacon, cut into small dice, until lightly browned, and add 1 tablespoons finely chopped onion. Cook the mixture for a few minutes longer. Add 1/2 cup of vinegar, 1 teaspoon salt and 1/4 cup sugar and pepper to taste. Bring the mixture to a boil and pour over the hot sliced potatoes. Serve the salad hot.