Diagnosis
Insufficient airflow is the primary cause. The dampers control oxygen flow to the charcoal.
How to Fix It
Check three dampers. The main lower draft door on the charcoal bowl must be fully open. The two sliding dampers on the back of the lid, one for each zone, must also be fully open for maximum heat. Ensure the lid is fully seated. Use high-quality lump charcoal or briquettes, filling the grate completely.
If That Didn't Work
Inspect for ash blockage. A full ash pan or ash clogging the lower draft door intake severely restricts airflow. Empty the ash pan and clear any debris from the door opening.
Heads Up
Ambient temperature and wind affect performance. On a cold or windy day, you may need to use more charcoal and position a wind block to reach higher temperatures.