Scrub beets for soup and cook in boiling water until tender, about 45 minutes; drain and discard water; cool. Peel and cut each beet into eighths. Scrub small beets; grate; cover with water to soak. Remove meat from soup; set aside. Strain soup into another pot and add cooked beets, cabbage, leeks, potatoes, tomatoes, tomato paste, vinegar, sugar, beef and bacon. Bring to a boil and simmer 45 minutes. Cut kielbasa into chunks and add with navy beans to soup. Simmer 20 minutes more. Mix flour and butter together to form paste. Stir into soup to thicken slightly. Strain raw beets, saving liquid and discarding beets. Add beet liquid to soup. Additional sugar or vinegar may be added for sweeter or more sour flavor. Slice meat and arrange in individual soup bowls. Pour hot soup with vegetables over meat. Garnish each serving with a dollop of sour cream, if desired.