[THEFERMANATOR]

Does it eventually smooth out and sound like it has lost a cylinder? This sounds an awful lot like a fuel issue where your losing one cylinder. Although it could easily be a switchbox or stator issue. When it does it next time shut it down while it's doing it and go back and pull all of the plugs out. Look for the one that looks like it's not firing or out of the ordinary. If they all look uniform, but the problem is still there I would suspect the stator's high speed side. If one of your plugs looks really light in color then you know which carb to check. If one plug looks wet or fouled then check the ignion for that circuit. You need to isolate the problem so you know which are to address.