Welcome. Hey, you need to rev it above 4000 at least once every time you ride the beast. This thing has secondary injectors that kick in around 4500 rpms. At 8000 rpms and 80% throttle, the secondaries are contributing nearly 75% of the burned mixture. However, if you don't make use of them often, they will plug up and the bike will run like it's in B mode all the time. I suspect that's what happens when you click from A to B mode, it just shuts off the secondary injectors.
Believe me, you don't need and won't miss B mode. It's so pathetically boring. However, if you are trying to change it while riding, it won't work. Motor has to be idling and bike has to be in neutral to make the change. I have the original owners manual, and that's what it says about it.
I have a B-King and a much modified M109R. I ride the king quite a bit more than the Nine these days. Much lighter and more zippy bike than the Nine. I love my Nine, don't get me wrong. But the King is a more exhilarating bike to ride.