I got a WSK last week and I am having a bit of trouble keeping the temps stable. With my burn-in I lit a full chimney, let it get rip-roaring hot. I ran it for about 45 minutes at 500+. I wanted to check it for air leaks so I locked it down and tried to snuff out the coals. It stayed over 400 until the coals were expended about 2.5 hours later, the coals were spent and I was unable to shut it down. Next burn I was determined not to overshoot my target temp but I did want to run a full load of coals to try and get a handle on temp control and simulate a 15 hour brisket cook. I have a WSM, so I used the charcoal ring and filled it. I nestled one tumbleweed in the center of the coal basket, I lit it and let it burn until it was expended (about 5 minutes) with the lid open and bottom vents full open. I then closed the lid and left the bottom and the top vents open until the temp raised to 200, at that point I move the bottom vent to the smoke position and opened the top vent about half way. It shot right past my desired temp to about 325 and wanted to stay there. Not wanting another uncontrolled overshoot, I shut it down (top and bottom vents). I opened the lid to let the heat escape, brought temps back to 200, at that point the coals started to die (about 10 minutes) , I could tell because they started kicking off the smoldering white smoke. I would gradually open vents and it would eventually overshoot again. I repeated this process many times, I eventually got to the point where the bottom vents were only a quarter of the way between shut and smoke and the top vents were open maybe 1/8 to 1/4 inch and it still wanted to sit at 300+. At that point I got tired of messing with it, it was getting late and I wanted to go to bed. I hooked it up to my fireboard and went to bed. I set the fireboard to 275 and left the top open 1/4 inch. I used a pit viper fan with the internal fan damper only half open and the fan set to run no faster than 50%. I didn't want to overdraft the coals. The fireboard struggled with controlling it as well. After about 2 or 3 hours of yoyo-ing around 300-325 the temp finally settled in at 275, it ran that way for 14 or 15 hours until the coals were expended. Why am I having such a problem getting it to low and slow? Air leak maybe?