how do you ride? Don't take offense to this just asking to help you out. Do you ride WOT all the time? Slow and with traffic never really winding the bike out? A slight mixture of both but leaning towards one or the other? Be honest.
The reason I ask is maybe there is some carbon build up in the engine. Does the Bird run hotter than it used to? Has your mileage decreased noticebly from the day you bought it? How did the plugs look when you changed them; Black, white, scorched, normal, pieces missing?
I'm not really in depth on this bike just yet but does the Bird have a lot of emmisions crap on it? Like a charcoal filter, or PCV valve. I've seen cars in our shop that look great on the outside (engine wise) but run like crap. Tear them down and you could literally fill a gallon bucket with carbon and suite (sp?).
Just some food for thought. I doubt it even has anything to do with it....