I like a little black smoke coming out of the stack but somebody should explain that the reason to reduce the black smoke is not environmental it is to reduce the soot from the smoke from coating the tubes and reducing the boiler efficiency.
I was always told to add coal to just one side of the fire alternating sides each time. The hot fire on the side seems to burn off the smoke from the fresh side fairly well. I think letting in cool top air and putting a hole in the fire are not very efficient things to do and are hard on the boiler.
Got a bad Casting from Stuart in England. Sent them an email with a picture and they sent a new casting. No problem. PMR is a good company they should do the same with those picture.