Using a weber 22" kettle I attempted a 5 hour roast/ smoked whole chicken. First three hours were at 225-235 f and then the last 2 hours were to be at 265-275 f. I built my normal snake I've used in Brinkman grills and other cheapie grills half way around the grill with KBB two rows of 2 briquettes one on top of the other and then a single row on top of that with a larger pile near the end for the higher heat at the end of the cook. Lit it off with 10 briquettes from the chimney. Grill stabilized after 25 minutes at 250 then I closed my vents at brought it down to 225. First three hours no issue held temp fine however when I opened the vents up I couldn't get the temp higher than 250 which quickly dissipated to 235ish. Ended up after two hours with no luck pulling the bird and finishing in the oven. Bird was at 145 internal when pulled before oven. Any clues how to get Temps back up so I can finish on the grill in the future?