I was having similar problems with a different stove and setup, but maybe what I tried (thanks to the forum) can help.
I thought I didn't have enough draft in this old habd fired bit furnace. I added a barometric damper this year and so far in early test runs am doing much better.
It seems I had tto much draft, but it seemed like I was never getting enough draw, so I often had the lower draft control and ash door open. I got heat, but had trouble with a long lasting fire that didn't cool off too much to make heat and was hard to add coal/reignite.
I was sending too much heat up the chimney.
I also followed suggestions posted here and move the hot coals to the side and load fresh coal on the other side of the box. I add a lot of coal at once, use poker to make sure there are open airways in both the hot coals and the fresh coal, and then open the manual damper (I have both mpd and baro) and the ash door until the fire stokes up and starts the new coal. About 20-45 mins. Then I close mpd about 1/3-2/3 of max and close the ash door with the draft aboult 25-50% and the fire seems to settle in nicely.
This part may be of particular interest.
My furnace is Not air tight and I have a tall masonry chimney. A baro helped me stabilize my draft. Having and maintaining a good draft allows better burns and helps pull smoke out the chimney , even when the mpd is cut way back.
With a short chimney, you may need more draft, then use less primary air for a better burn and heat. Try that loading procedure I mentioned. It was posted by some one from an old magazine article.
Hope this helps.