Insufficient temperature on mini WSM

I'm doing my first cook on a mini WSM. I got it to 225 by adjusting the top vent, leaving the bottom vent completely open. It's the model,with the vent on the bottom, so I added the can with holes in it to keep ash from clogging the vent.

It's about fours into the cook and I can't get the temp over 200. I've got the top vent all the way open and have stirred and added coals multiple times. It's been too cool for about 2 hours. There's no ash in the bottom vent. I can't tell if it's up to the top of the tin can because I can't dump the coals out to look.

I'm cooking two butts, 16 pounds total. One butt is on each rack. The temp probe is a couple inches from the meat and did read 225-245 early on, so it's not that the meat is making it seem cooler.

Any suggestions? I have expanded metal to put a ring around the coals grate for next time but can't think of anything else to do.

Thanks!

I can start more in my chimney and will dump them in to,see what that does.

It was now above 250 and I finally had to close the top vent again. I don't know what happened there. I put some more unlit briquettes on just now to get them going and it hasn't lowered the temp enough to make me open the top vent again.

To answer your question: no, I had not put any more lit coals in. I took the chimney out there to do it but noticed the temp finally climbed while I was writing the post and reading your replies. It's still about 250, but that's probably OK to catch up for the period where it was too cold. It should start cooling off now that I have the vent partially closed again.

I have the recommended 12.5" clay terra cotta saucer as a diffuser. I have a foil pan on top of that to catch drippings, but there is no water in it.

I'll regulate from the intake and leave the exhaust open next time. I just got the smoker part made and didn't have time to put a decent handle extension on the bottom yet.

Forgot to answer your earlier question. I'm using my Polder corded kitchen thermometer and just have the probe sitting on the top grate away from the meat. I don't have the slick wireless setup with two probes yet.