ogaugeguy: I have the Birkshire #765 NPR and no where in the operators manual does it say anything about the chuff rate only the volume. I assume it is set at the factory. Word of caution on the smoke unit>It is very easy to overfill so be careful. BTW my fan for the smoke was broken when I receive the engine so I had to send it back to Lionel Service. Everything OK now. LarryWhat is the chuff rate of the Lionel FlyerChief Polar Express locomotive? Can that chuff rate be either mechanically or electronically altered to increase it?