In a small bowl combine the sugar, paprika, pepper, curry powder, and salt. Rub over ribs, coating well. Place ribs in shallow pan. Cover and chill for at least 2 hours or up to 6 hours.
In a covered grill, arrange medium coals around a drip pan. Test for medium-low heat above pan. Place ribs, bone side down, on grill rack over drip pan but not over coals. Lower grill hood. Grill about 1-1/4 hours or until tender, and adding more coals as needed.
Meanwhile, for sauce, in a medium saucepan combine brown sugar, vinegar, onion, mustard, garlic, honey, liquid smoke, and celery seed. Bring to boiling; reduce heat. Cook, uncovered, for 25 to 30 minutes or until slightly thickened, stirring occasionally. Brush sauce over ribs occasionally during last 10 to 15 minutes of grilling. Heat any remaining sauce until bubbly and pass with ribs. Makes 8 servings.