I have an 89' Phazer. It's always gone like a raped ape until one day end of last year. It just started bogging real bad almost like it was choked. If I take the airbox off it goes great. I've tried running it lean, thinking it was getting too much fuel and not enough air but it didn't make any difference. I tried running it rich, I tried removing the exhaust, tried new spark plugs, tried cleaning the carbs, cleaned out the airbox, cleaned out the read valves. None of this made any difference. I'm stumped! Any ideas?