I have my Bachmann 2-8-0 with the chuff rate in CV116 set at between 75 and 100 and usually run it with the speed of 21 showing on my throttle. Don't know what the default setting is.
Did you try to read back what was in CV 116 on a programming track? If I recall it is about a value of 80.
Plug in 100 and see if it is close to where you want it and adjust up or down from there to correct it if needed.
Unless Soundtraxx has changed the range of possible values for CV116, it has a range from 1-255. I find that if I start with a value near 140, I usually have to work my way up from there to get four chuffs per revolution.
Before you do any of this, you should fine tune your motor's drive characteristics by fiddling with the CV's near 208-212...I think those are the numbers.
-Crandell