What thermometer are you using to determine your chamber temps in
the Kettle? A lid thermometer, or a Maverick type probe on the cooking grate?
The reason I ask is I found there can be up to a 100F difference between the lid and the grate in a
Weber Kettle. Once I understood that, I abandoned common guidance about controlling the temp with the bottom vent. I started using the top vent to control chamber temps in my Kettle. It greatly evened out that difference between the grate and the exhaust. The problem with using the top vent though is stale smoke. I adapted to that to ensue flow through.
I'd load
the Kettle for indirect heating, only put about 8-10 hot coals on the cold ones/wood chunks, leave all my vents full open. Although I had a Smokenator, which is basically a heat fence, you could use charcoal baskets just as easy.
When the chamber temp of the grate level was within 25F of my target, I'd start closing down the top vent to about 1/4 open, but not before dumping the white smoke in the chamber by taking the lid off and putting it immediately back on. I'd do that about 2-3 times until I saw TBS, then I'd load the meat. By keeping the bottom vents full open, dumping the white/grey smoke, and waiting until you see TBS, you don't get that creosote or ash buildup or the stale smoke taste on the meat.
I could get about 90 minutes of stable temps before the temps would start climbing or dropping. I wouldn't make any adjustments to the vent until I was 25F high away from my target, or 10-25F low. I got to where making small, 1/16" changes to the top vent would change the chamber temp by 10-15F. Once it stabilized, I could get another 90 minutes. I'd usually have to add additional cold briquettes around the 4-6 hour mark.
Just another way of looking at it that works on
the Kettle.
