Cook the elbow macaroni as directed on the package. Rinse in cold water and drain well. In a large bowl, stir together the mayonnaise, vinegar, mustard, sugar, salt, and pepper. Mix to dissolve the sugar. Stir in the cooked pasta, carrot, bell pepper, and onion. Mix well. Cover the bowl and refrigerate for 1-2 hours or until well chilled. Stir before serving. Add a little additional mayonnaise if the salad seems dry after chilling.