I've been having some problems with my 18" WSM running hot and getting away from me. I do have a stoker and it works great for a few hours, but whenever I need to open the lid for more than a few seconds it heats up to around 300+ and has a hard time cooling down. Yesterday I was doing ribs 3-2-1 and temps where perfect until I had to pull the racks out to foil them. By the time I got all 8 racks off the temp on the smoker went up to 300 and it never cooled down. I think the lowest the temp got was around 230 and held for the rest of the cook.
Not sure if i'm using too many coals or if it's the wood chunks that's causing the problem, but I basically use 1/2 of a chimney of lit coals and around 2 chimney's of unlit coals. I push all the unlit coals to one side and drop in 3 softball size chunks of soaked wood on top. Then I pour in the half chimney on the side that doesn't have any coals as at.
On a side note where is the best place to put the temp probe from the stoker to get accurate readings.