I have a 18.5 inch WSM and have a difficult time controlling temperature. I want to hold 220 - 230 degrees, but usually I run 260 - 280 degrees at the cooking grate.
I use charcoal briquettes. I start with 1 - 2 chimneys unlit, topped with 1/2 chimney lit; Minion method. There is water in the pan, cold or hot, matter not. A few chunks of wood are burried in the unlit charcoal and a couple chunks on top of the hot coals.
The top vent is always 100% open. I start with the bottom vents 100% open, and rapidly bring them to 10 - 25% open.
What can I do to lower the temperature? Start with less unlit charcoal?