Cover the grill. After an hour, check the chicken and refresh the coals if needed. Keep checking the chicken every 15 minutes, until a meat thermometer inserted into the thickest part of the thigh reads 160°F - 165°F. If you don't have a meat thermometer, poke the thigh deeply with a knife, if the juices run clear, not pink, the chicken is done. Cooking times will vary - a 4lb bird will take about 1.5 hours.