I had a smoke problem with my Anchor Stoker, probably built similar to your combustioneer.
I sealed the coal bin to the auger with blue RTV sealant, then sealed the gear box to the bin, and then worked with the door gasket, should have replaced but haven't found a good material of the correct shape, smoke has stopped.
Some stokers had a 3/8 tube from the air supply, after the blower before the twyres, and into the coal bin, this puts a small positive preasure in the bin keeping the smoke from coming down the auger into the bin. This cure if done with to much air would probalby cause the fire to chase the air up the auger, in other words be careful about using to much air.
Berlin would be a great resource on this subject.