Not Hot Enough

During test runs for my first smoke/BBQ (see other thread), the max temp I've been able to register is 250 degrees. I'm trying to spatchcock a chicken and am going to need 350. What gives?

Weber SJS
Both vents fully open
Tomato can with 8 vent holes punched on side, 6 on top to cover ash catcher
Basket full of coals started in a chimney (can't get hotter down there)
Standard Vasconia pot diffuser only
Thermo just below top rack]
It's a windy day but I would think I would at least come close, given the amount of hot coals I have here.

What am I doing wrong?

Update:

When I take the diffuser out, the temp shoots straight up to 350 and holds. I think I'm just going to try that. With the chicken on the lower rack (to free up the upper for sides), I'm a bit worried about flare ups, but maybe it will work out.

FYI, it's windy today. Winds 23 mph with gusts to 35.

HLarson3 said:

Update: When I take the diffuser out, the temp shoots straight up to 350 and holds. I think I'm just going to try that. With the chicken on the lower rack (to free up the upper for sides), I'm a bit worried about flare ups, but maybe it will work out. FYI, it's windy today. Winds 23 mph with gusts to 35.

Click to expand...

You nailed it. That's what you have to do, remove the diffuser to get the 300+ temps. Doing that produces a flavor some like and some don't, and that's drippings hitting the hot coals. If you don't like that flavoring, a throw-away aluminum pie tray will catch the drippings without lowering your temp. When I want 400+ degrees (wings and whatnot) I leave a cooking grate in my SJ and set the pot on the grate. That provides a considerable amount of air to the coals which makes a hot fire, but burns out pretty quick