Wash and pat dry chicken inside and out with paper towels. In a small bowl mix taco powder with sugar. Rub into chicken inside and out, making sure that you also rub it underneath the skin. Let marinade in refrigerator overnight.
In a small saucepan simmer 3/4 cup guava juice and tequila. Simmer until mixture is reduced to 6 ounces. Pour liquid into empty beer can by using a funnel. Set chicken over beer can. Brush with melted butter
Light barbecue grill until hot. (I used a gas grill). Turn off one burner and place chicken carefully over the unlit burner. Close hood, lower heat to medium and let chicken grill for 1 1/4 to 1 1/2 hours or until chicken is crisp and the thermometer reads 180 F. If chicken browns too fast, cover with foil.
Make glaze: simmer remaining 1/4 cup guava juice with soy sauce, chipotle and lemon juice in a small saucepan until slightly thick. Brush some glaze over chicken and let stand 5 minutes to rest. Any leftover glaze can be served as accompaniment to chicken.
Be very careful when removing chicken from grill and can. Place chicken on a large plate, garnish with cilantro.