Drain liquid from beans and mix together. Fry bacon until crisp and break up into the beans. Fry onion, chopped, in the bacon fat and add to the beans. Add to the fry pan with remaining fat. Brown sugar, mustard, and vinegar. Boil down to 1/3 about 10 minutes. Mix with beans. Bake at 300 F for 1 1/2 hours.