Brown roast on both sides in hot oil in a large Dutch oven. Combine sugar, ginger, cloves, allspice, bay leaf, salt, pepper, onion, 1 cup water, and vinegar; mix well, and pour over roast. Cover and simmer 1 1/2 to 2 hours or until roast is tender, turning once. Remove roast to serving platter.
Stir remaining water into flour; stir into pan drippings. Cook, stirring constantly, until thickened. Pour over roast.