Hi, I think it's the same problem ,as I had and post in "UNBURNED COAL IN MARK III" unburned coal (left overs) in coal stove MARK III
It's VERY helpfull for me with my MARK stove and I hope it willl help for you. Rberg right, Mark has air vents on top and bottom sides closed by gasket rope (good for wood , bad for coal burning and do not protect glass from cresote build up-glass get dirty anyway).
Check ashes on grate, can you see reflection of gloving on ash pan metall when you shake ashes down?when you put more coal ? if not shake more, Reading has a lot of ash, I'd say 20-30 percent.
When loading coal let lower door to be open (you can clean ash pan in that time )10-15 min to get fire started in full bed .
I open lower door knob open 2 turns , 3 too much ,1 is not enough (for 30 outside, NJ))
Again , read "unburned coal"post, guys so smart there.