Sweet potatoes and fire get along perfectly. Don't be confused by the labels in the produce aisle. For the best flavor you want buy what the local grocer calls yams . They aren't really yams at all - good luck finding a real yam. If you substitute lemon juice for lime juice you lose a lot of the flavor. Getting the right heat and the right distance from the flame takes some experience and experimentation. You might want to practice with one piece of potato at a time until you get it right. You should use a vegetable grill rack because the pieces of potato have a tendency to slip into the fire.