Cook sugar, 1/4 cup cold water, and corn syrup in a small heavy saucepan over medium heat, stirring constantly, 30 minutes or until mixture is caramel colored. Remove from heat.
Add remaining 1/2 cup water. (Sugar mixture will clump but will dissolve when heated.) Bring to a boil. Boil, stirring constantly, 5 minutes or until smooth. Stir in ground cinnamon and cloves.
Pour over orange and grapefruit sections. Garnish with orange curls and cinnamon, if desired, and serve warm.
*3 1/3 cups jarred orange sections, drained, and 5 cups jarred grapefruit sections, drained, may be substitutued for fresh fruit.
NOTE: Caramel syrup can be made ahead of time and chilled. Reheat in a saucepan before serving.