Bob,
I often forget that the smoke unit is like an old oil lamp in many ways. It uses a consumable wick conducting smoke fluid that is set to smoldering by the heat element. The wick will char/burn/toast over time. The build up of the carbon "scab" as I call it, does not conduct smoke fluid. In fact it blocks it from reaching the heat element. The carbon debris needs to be removed from the wick and the heat element. Then the clean wick material is stretched and moved up against the heating element again.
The only parts Lionel would service are the heating element, the fan motor, and any board controlling them. The cleaning of the wick is our maintenance responsibility or whoever we pay to do it. Once it is newly clean, smoke will pour from the smoke stack. See the pictures of my Erie PA units. Gunrunner John commented that it was too much smoke like real engines needing service. Over a short time, the smoke returned to a normal level.
You can see the fan duct work is half way up from the bottom of the reservoir. It would take a good amount of fluid to block the opening.
Wait for Gunrunner John to answer any other questions. I was forced into servicing them because the engines did not smoke well, and I bought them on Ebay without a warranty from Charles from Nicholas Smith.
My very first train set was the Erie PA AA Freight with four freight cars that my Dad put on a board under my crib. I am now 69 years old, and the train is on my shelf.
Sincerely, John Rowlen
