Where do you measure and what does your dome thermometer do while you have a runaway WSM?
How fast is the spike? Are we talking 5 minutes to go from 250-300? 60 minutes?
Where are your vents before it runs away?
How did you fill your wsm? Full bag of charcoal in the ring?
When I completely close off two of my bottom vents, I have a charcoal burn that moves towards the side with the only open vent. A pit probe in the "hot zone" over the open bottom vent of the WSM with the charcoal burning directly underneath can easily go to 300F, while the rest of the cooking chamber is more in the area of 225-275.
When I see a spike with the pit probe, I look at the dome thermometer. A true 300F spike should have at least 275 at the dome. If not, I discard the pit probe measurement as faulty, for example due to charcoal burn.
If you measure the pit temp next to the meat, you will read 10-30F lower than the actual pit temp for quite a while. Cold meat cools the area around the probe. Meat "sweats" water during the cook, and especially during the stall, further cooling the area around it. 250 next to a big piece of meat can be more like 275-300 in actual pit temperature.
Lastly, on getting a big 22 WSM down in temp: Yeah, its a pain. Somebody here in the forum told me the theory of lit vs unlit charcoal. Once your WSM is at 300, you have a bunch of charcoal lit to get to that temp. Getting the temps back to 250 requires you to have fewer coals burning. But what you control is airflow. So to get thentemps down, you close the vents until coals are smoldering. Temps go down. If you then go back to any sustainable vent setting, you still have too many coals lit and the temp immediately spikes again. You need to get the amount of burning coals down. I have not found a good recipe yet. Coals would need to either burn out without lighting other coals, you would need to extinguish coals by starving them of oxygen and letting them cool down significantly, or you may need to physically remove coals. Just ideas.
