The brass cup on the MTH smoke unit is a small diameter and will not fill the engine stack. I took brass tube from hobby shop or do it your self center that had an outside diameter to fit the engine stack. May have been 3/8" you can measure the unit you took out. The inside dia almost fits over the smoke unit brass cup. What I did was use a pipe fitting tool to widen the end of the tube, to get it started over the cup, then press on with vise.
It can't be too long other wise you can't fit the smoke unit in. So this takes some measurements. Basically works to help hold smoke unit in the stack and makes sure adding smoke fluid goes into the smoke unit. G
