Fisher smoking out of intake

Sounds like you're describing a flutter.
It will typically stop if you open air intake fully. Then after flue temperature rises and more oxygen increases the out gassing, the balance is achieved again at a higher temperature and it starts again. I couldn't stop it here either. I think the small volume of the stove being less than the chimney is the pressure changes not absorbed by a larger area of firebox. To compound the problem, every stove has resistance of the stove itself. The most resistance is due to the intake size. The chimney makes positive draft (or negative pressure) and the connector pipe, elbows and spark screen reduces draft or raises the pressure in flue. The damper is a variable resistance. Since the formula changes due to flue gas temperature above ambient temp and chimney diameter, arbitrary numbers are used with 100 as a base for chimney flue 20 feet high. You then subtract for each resistance in the system by the numbers given in a table. Example; 45* elbow = .2 to .7, 90* elbow = .5 to 1.5, 6 inch dia. pipe = .05 to .08 per foot.......... The total you come up with is "Resistance coefficients of chimney components". Then you take into account chimney height and diameter to figure relative capacity. There are graphs with resistance coefficient and temperature and capacity at certain temperatures. Then you have the stove resistance. If everything calculates for one stove, another may not when the final resistance is added. Stove air-inlet damper effective resistance chart (damper fully open) shows this for your smaller stove;
4 inch pipe; 2-8 5 inch pipe; 5-20 6 inch pipe; 10-40 7 inch pipe; 20 -80 and 8 inch pipe; 30 -120. You can see how the resistance increases as the flue diameter is increased. This shows reducing to a 5 inch flue decreases air inlet resistance by half and no doubt would cure the problem. I'm sure Fisher didn't want to make them with a 5 inch outlet and require a 5inch flue. They wouldn't sell many stoves that way.
The table for the larger stoves gives half the resistance for each pipe size due to having twice the size intake area.
Try laying fuel tighter to decrease oxygen through it and slow burn rate to see if it stops the flutter totally.

I got into all this formula stuff adding the Smoke Shelf Baffle that was designed for the double door stoves to the single door stoves.
A Honey Bear would be your perfect answer ! Plus they are baffled and an optional blower can be added that blows forward across the top. (blowers new in box still available)
Single door, double door, 4 legs or pedestal;
Legs or pedestal not installed during reconditioning.

Optional Bear Legs installed. Blower hangs on bottom of shield that is curled at top directing flow forward.

Double door on pedestal.

They all use this internal baffle plate that doesn't affect fuel capacity;



This was not burned properly at all. Stove was full of soot when I got it with half burned pile of huge chunks stuffed in it. They gave up. I got it for $200 !

 

It sounds like from what you are saying that a restrictor plate of sorts might help a lot. The problem did get worse when I removed the key damper which even when open provides some level of resistance. Maybe a partially closed key damper or just a section of custom fabricated 5" pipe might help balance out the suction vs. resistance struggle.

 

The chimney sounds like it is a little on the short side for trouble free operation, 14 feet would be marginal for some stoves.

 

Had about 18 feet on my Nashua and could start the fire with the door closed.