Lionel spitting smoke units.

Imo it seems that the fluid doesn't fully absorb into new wicking.

Not unlike a new sponge initially repels water

I've found my smoke units work better after numerous heating cycles over time which" seasons" the wicking

Worse, there is fluid in the smoke/ air. Being pushed creates "high pressure air".

Exiting the small hole creates an instant pressure drop, which aborbs heat from the air and "nozzle" tip both. This temp drop causes instant condensation of moisture in the air, be it water or oil or whatever.  Your air conditioning and fridge do this. A propane unit heats for pressure vs pumps.

Much like blowing from your air compressor or long runs with an air tool where the tips/exhaust ports freeze.  (or nearly too small a carburator frosts over)

Restrictions of id within pnumatic plumbing are natural moisture gathering points.

My issue with the dual chamber units is when one is smoking, there is blowback through the other chamber.  I have one here now, I can't seem to stop the whistle steam side from bleeding out it's fan intake when the main stack is blowing smoke.  IMO, the dual chamber smoke unit is a flawed design!