If blowing in it won't "toot" it, I think the reed alignment might be bad from agressive cleaning
Feel the airflow amount from the reed port. Direction o.k.? Is the impeller close enough to the intake, a hair gap is needed, too much and chamber air is spun vs a draw from outside.
Does the whistle chime then "tweet out" (too much air) or never chimes? Never? Try to cover a small portion of the port with finger/tape (try the short length then along the high side of the port (non beveled). Reducing the port size reduces air needs. If changing the port size doesn't give sound, I'd have to think the reed's beveled angle was filed on or something.
To rule out a weak rpm motor & lungs both, try a vacuum's blower 
