Turn grill to high (or 500 degrees), once it reaches 500 degrees clean it off good with grill brush. Once the grill is cleaned turn the heat down to 350 degrees ( medium high). On the stovetop in a small/medium sized sauce pan, on medium heat, add butter, vinegar, garlic powder, salt & pepper. Cook till butter is melted, stirring occasionally. Once grill has reached the correct temperature of 350 degrees place raw chicken halves on the grill and baste them with vinegar & butter mixture. Close the lid to the grill and cook chicken for 1 to 1(1/2) hours or until chicken has reached a safe temperature of 170-F (77-C) degrees, basting every 15 minutes.