Wide open just to keep 250 while using lump?
I just did sausage, baked beans and veggies using all lump, including a 3/4 chimney of lit.
When the temp hit 250 I closed 1 bottom vent and left the other 2 open ~1/8".
Half hour later (or sooner- I didn't monitor) it was 270, and stayed there for 2.5 hours. I removed the veggies and opened the closed vent a 1/4" and when I checked 30 mins. later it was at 325, when I pulled everything else and shut it down.
Many Webers inc. a cute-@ss 14.5 wsm; Vision C; & 1/4" all-weld Brinkmann Cimarron offset.