Grilled chicken can sometimes get burnt on the outside while the inside remains undercooked due to several factors:

1. **High Heat:** Cooking chicken over too high heat can cause the exterior to cook too quickly, resulting in burning, while the inside may still be raw. It's essential to adjust the grill temperature to medium or medium-high to ensure even cooking without burning the outside.

2. **Uneven Thickness:** If the chicken pieces are uneven in thickness, such as a thick breast with one side thicker than the other, the thinner parts may cook faster and burn while the thicker parts remain undercooked. Try to pound the chicken to an even thickness or butterfly thicker pieces to ensure even cooking.

3. **Direct Flame:** Placing the chicken directly over flames or hot spots on the grill can lead to uneven cooking and burning. Use indirect heat or move the chicken away from direct flames to prevent burning while allowing the chicken to cook through evenly.

4. **Lack of Oil or Marinade:** Without a protective layer of oil or marinade, the chicken's surface can dry out and burn more easily. Brushing the chicken with oil or marinating it before grilling helps keep it moist and prevents burning.

5. **Cooking Time:** Grilled chicken requires precise timing to ensure it cooks through evenly without burning. If the grill is too hot or the chicken is left on for too long, the outside may burn before the inside is fully cooked. Use a meat thermometer to monitor the internal temperature and remove the chicken from the grill once it reaches the safe internal temperature of 165°F (75°C).

6. **Flare-Ups:** Flare-ups caused by dripping fat or oil can quickly char the outside of the chicken. To prevent flare-ups, trim excess fat from the chicken before grilling and be prepared to move the chicken away from the flames if necessary.

To avoid burnt grilled chicken with undercooked insides, it's essential to control the grill temperature, use indirect heat when necessary, monitor cooking time and internal temperature, and take steps to prevent flare-ups. With proper technique and attention to detail, you can achieve perfectly grilled chicken with a juicy, flavorful interior and a beautifully charred exterior.