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Smoke: 
It's all about flow.  Flow of current, smoke fluid, and air.  Current 
flow - - the five-wire arrangement works best.  On Franklins and others that count on the chassis/tow-bar add a direct wire from the front truck.  A smoke coil of the correct resistance (35-53 ohms) that is not in contact with the metal chamber is a must.  Any doubts, remover leads and measure using VOM.  Adjust the location of the coil or replace it by rewinding a new one on some fresh wick material.  Smoke fluid flow - - a soft wick capable of sustained
capillary action from tip to and through the coil is required. (I'm 
talking for no jok'n it's smok'n performance).  You can revive a minorly impaired wick with alcohol, WD-40, track cleaner, etc, down the stack (then let evaporate overnight, unless you want engine flambe).  But I've found you usually have to open the unit and inspect the wick.  If petrified with old fluid, gently unravel and let soak in a baby food jar of isopropyl alcohol (kept safely away from flame, spark, etc.).  Rinse with water, blow dry with hair dryer.  Should be fluffy again.  If too far gone, replace with 2' piece of new wick and rewind a new coil at it's mid-point.  If the wick is charcoal through the coil.  Replace the wick and coil.  The type of fluid can optimize the performance of a good wick and coil combo, but not 
make up for any shortcomings with either.  I like Lehigh Valley Train Service's S-Gauge fluid best (but it's no longer made), 99.9% pure lamp oil next best (some after odor, lace with cedar oil helps), ProtoSmoke next best (made by LVTS for MTH), and personally find SuperSmoke too thick.  Air flow - - must be unobstructed from entrance to exit.  Inspect your system from the drive gear and bell crank through the stack.  Piston and cyclinder should be clean
and make for reliable compression of air into the hole and the forward end of the cylinder.  That hole needs to be unobstructed.  The chamber it leads into, clean and clear of dirt, fuzz, spider webs, etc.  The tiny hole from the Choo-choo chamber into the smoke chamber must also be clear and clean.  The air path through the smoke chamber should be unobstructed as much as possible even by the wick and coil (pay attention to that as you reassemble).  Obviously the hole at the base of the stack and the stack itself must be wide open.  For SIT models, add to these items an unobstructed rubber hose of the right diameter, material, length, and path from the tender through the boiler shell, along with bellows inspection, repair, replacement and routine motor care.  By taking the right amount of time, precautions, and care you can set off smoke alarms, or chase
mosquitos with an AF smoke unit.  Enjoy.

David Horne