Pumpkin Chili

3 pounds lean ground beef
2 cups fresh pumpkin, cubed in 1-inch pieces
1 can (15 ounces) kidney beans
2 medium onions, diced
3 cans diced tomatoes
2 tablespoons chili powder
2 tablespoons sugar
1 teaspoon salt (optional)

Brown ground beef. Drain fat. Put ground beef into large cooking pot, add each ingredient, and cook on low heat for 90 minutes. Serve with sour cream.