In large skillet saute' beef and onion, over moderately high hear stir occasionally, cook until meat is no longer pink. Drain.

Stir in ketchup, vinegar, lemon juice, Worcestershire sauce, mustard, paprika, sugar and salt and pepper to taste,.

Cook uncovered over low heat stirring occasionally, until thickened, about 30 minutes.

Divide mixture among hamburger buns.