Had a minor epiphany today while working on some locos for a client: I think a lot of the problems with air whistles, particularly pre-and-postwar models, is that they're idle a lot of the time. Thus, the commutators and relays oxidize, the bearings and lubricants gum up and, in general the things suffer from only operating a second or two at the time.
I experimented with a 2046W and a 6654W. Both had been serviced, but both were still sluggish and required high voltage to operate.
The procedure was simple: One at a time, with no engine present, I cranked the voltage up, held the whistle button down and did a one-one thousand count up to 60 full seconds. That is a LONG time with an air whistle blowing in your ear! 
The results were astounding. Both whistles were a lot stronger and required a much lower voltage to blow clearly and loudly!
So, if your air whistle isn't performing as well as it might, an Italian tuneup might be in order.
Try it, you'll like it!
Mitch
