There are cheap conversion kits available that have a low value resistor and some fiberglass webbing that replace the old coil to help them smoke better. Have done a number of the conversions (kits are under $5, but you have to get in there and pry the top off the smoke unit to do the job). Make sure that the little hole in the bottom of the chamber is not clogged - many postwar locos are jammed full of pellet residue - seems like once they are plugged, it's almost impossible to burn out the jammed hole.
