Racie35;
Plates and registration are not required on these motorized bicycles here in Illinois. That's the good news.
But they might be required on a Whizzer since it won't fit the criteria for a 'motor assisted bicycle'. At a guess I'd say that it probably needs to be registered as a moped.
But most States and localities will honor the laws of the home State for visiting motor vehicles. You'd be wise to have some proof of residency with you.
And, like so many other places, law enforcement around here doesn't seem to care very much about these bikes as long as the rider isn't giving them some reason to care.
So I'm guessing that you'll, technically, be non-legal. But I'll bet you can get away with a visit and a bit of riding.