CamFan is the member name from the Georgia fabricator. He was a welder at the largest Fisher fabricator in the country that married the step daughter of the business owner. He and his wife are now the owners of the Hearth business at the same location in Watkinsville Georgia, with some new old stock still on the shelf they have saved. If you type @ before a member name it will list the members to click on and give them a message like this;
@fdgraham54
OK, since the chimney and connector pipe has worked fine, There has to be a blockage in the intake or exhaust. I would look for a blockage in the intake of the stove. Slide the intake adjuster open and make sure the sliding plate opens fully. Try a piece of wire, coat hanger, anything that will go into the intake and try pulling anything out. As bits of wood and ash pop off logs they can bounce off the door into the slot. I call the box on firebox bottom the intake air box that houses slider plate. That may be blocked. Stoves in storage get mouse nests and acorns, you name it. Not the case if this has been in a rodent free home.
Top of air box on firebox bottom. Intake slot across front shown. An ash vac would be best, unless you have an old vacuum you don't care about. I have a simple plastic bucket you fill with water that is for vacuuming spackle dust that blows the fine ash into the water saving the vacuum. It was cheap and works well when vacuuming a firebox to re-brick. Straws or a piece of vinyl tubing or hose taped to vacuum pulls lots of stuff out slot and intake air opening.
The Goldilocks pedestal has a trap door under the ash fender that swings open and needs to be cleaned at least yearly. I've had mine fill up, but never to the point of blocking the air intake. Goldilocks is the only model that has it since the air opening is a much larger opening with a screen over it across the front. Ash drops into that easily.
If the flue damper feels normal, that is the only thing to block the exhaust after cleaning. (other than not cleaning the spark screen if equipped at top) The flue damper plate can rust away or rotate on the shaft allowing it to rotate on the shaft instead of being secured to the shaft. You think it's open, but it's not. The spring on the outside of handle keeps it in place. Hitting the damper with a brush can knock the plate loose on the shaft, but you can feel it as it is rotated since it's not connected solid to the handle anymore.
Inexperienced wood burners will have problems with wet wood since it doesn't create enough heat to get the chimney hot enough for the proper draft and the combination of putting out more smoke causes the same symptoms as you describe.
I'm not sure if this stove should ever be flue dampered down. The flue damper is a chimney control that slows an over drafting chimney. Did you only close it slightly overnight? Overuse will cause creosote. A flue damper slows velocity of rising gasses which slows the incoming air, affecting the stove by slowing the burn. This affects how much air wash over glass as well. Normally it is left open, and control fire with intake air setting. Using a flue damper this way I was able to clean before and after the burning season. Using the flue damper I would have to clean mid season. The flue damper is required on the Fireplace Series stove with solid doors when using a spark screen.
A stove built for open door burning is brought up to temp, open doors with screen in place and start closing the flue damper slowly until smoke rolls in at top. Open slightly to allow smoke to evacuate, but slowing the airflow as much as possible through stove and up stack to retain heat. This becomes the only air control with doors open. It's good to have on any stove as an emergency brake, but shouldn't need to be used heavily under normal conditions with most Fisher stoves.
Without baffle more heat will be left up chimney creating a stronger draft and the stove will not get as hot. This reduces the resistance through stove, creating a lower air pressure in the stove allowing more air to push in. It may burn better showing there is a blockage not allowing enough air in with the pressure the chimney is creating with baffle in place.
These stoves aren't that heavy if you have a hand truck to take it outside and blast out the intake with compressed air, wearing a respirator if you have one or good mask and safety glasses. I think you may find a ton of crap in that intake box after 20 years. Do you have animals that lay around the stove to get pet hair in it?
