I'm about an hour and a half into smoking a 6.5lb pork shoulder in a Brinkmann Sportsman. I got the smoker up to temp, 225 - 250F, and then put in the water pan and meat. The smoker dropped off to about 170F and it not getting back into the 225F range. I have not done any of the pan mods yet. Any thoughts? I'm using "lump charcoal", even though most seems to be smaller pieces. I have the vent door open hoping to get more air into the coals. HELP!!!!