I'm still a rookie at this so I will answer the best I can. The temp you want to keep the smoker at is really quite dependent on the meat you are cooking. For instance, with the pork you are right its best to keep it around 225. In this particular cook, I was aiming to keep it around 225-250. When I made turkey on Thanksgiving, I was shooting for 350. The pork shoulder should be cooked well past the normal 140 or so that you would do in your oven for a sliced tenderloin. When you smoke for pulled pork you want to cook it low and slow in order to get the fat to break down and transform into a gelatin. (I'm probably getting this a little off so anyone else who is in the know please chime in). In order to do that, you need to cook it past 140 all the way up to 195 - 210. Thing is, with pork it will plateau for a while, usually around 160 - 170 and just sit there for hours before it finally transforms the fat and breaks through. You can tell this by feel too, in this case the two pork shoulders were bone in, and when they were done you could tell because the meat fell away from the bone. If I had gone and checked sooner, I probably would have been able to turn the bone inside the meat, which also would have said it was done.
OK, I'm more than kinda crazy so I kept a log of the temps in the past cook. There are three probe thermometers in the picture, and one thermometer not shown. One is not in either of the pork shoulders, that temperature is shown on the below graph as the "grate" temp. There was a candy thermometer through the top vent that measured the "dome" temp. These two readings helped to give a good baseline of what the actual cooking temperature of the smoker was. You can see that the general line if avg'd is probably around 250 but jumps a bit. The specific smoker I use is generally known as great for keeping temps, but on this day it was a little rainy and quite windy so it made it hard to keep the temp a little more constant. Also, when it spikes up towards the end I had added some new hot charcoal I had lit in a chimney starter.
There is a probe inside the pork shoulder which shows as the meat temp (yellow line). The yellow line shows how the meat plateaued for a while, and then regained a climb up into the target temp range. Where the temp drops about halfway through the cook is when I turned the meat and placed the probe into a different part of the meat. So the change is because of the different placement. I took the pork off at around 200 degrees and 16 hours of cooking.
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To explain the other line at the bottom, its the Dome temperature minus the Grate temperature. I think you want to keep a straight line here.
