I've got a set of Hooker Tuned Flow that I replaced with a set of Monster Ovals. I keep them for the time I want to be wicked loud. Momma don't like them, because they grate on her ears on long rides.
To tune them, you loosen the adjustment screws, and rotate the internals, so the that the cut line lines up with whichever setting you want. I used to run mine with reduced flow on the left and full open flow on the right. She liked it that way.
A Google search will yield an owner's manual. If not, I can post one...
Enjoy,
Rich P