In a pot on your side burner cook beans until crisp and tender. Drain beans. Fry bacon until crisp and drain all but 2 tbs. fat from the pan and add the onion. Saute for 5 minutes. Make thin paste of 1 Tbs. flour and 1/4 cup of water. Add flour paste, vinegar, sugar, bacon and onions to pan and cook until thickened. Pour over beans and toss. Cover and heat thoroughly.