Unburned coal in a Harman Magnum Stoker

I fired my magnum stoker up yesterday and it finally caught and has been going since. problem is I checked the ash pan today and it looks like cluncks of semi chard coal - when the stove is not using combustion air there is a nice even burn on the grate and all coals look lit. when the combustion fan kick on the flames shoot up like you would see in a gas furnace and everything glows much brighter. right now I have the combustion set to on 1 min off 15 - I have not connected the thermostat yet as I need to purchase wire for that. any suggestions on this. I do not think I am overfiring it but I am not sure?