Bring a large pot of salted water to a boil.
Add potatoes; cook until tender but still firm (about 15 minutes).
Drain, cool, and chop.
Place bacon in a large, deep skillet. Cook over medium-high heat until evenly brown. Drain, crumble, and set aside. Reserve bacon fat.
Add flour, sugar, water, and vinegar to skillet and cook in reserved bacon fat over medium heat until dressing is thick.
Add bacon, potatoes, and green onions to skillet and stir until coated.
Cook until heated and season with salt and pepper. Serve warm.