I sent my Vee2 to the dealer for the ignition wiring and ground relocation recall service, when I got it back it had developed an out of place vibe / buzz / sound... It sounded like when my gas tank is nearly empty, a subtle hollow buzz. However, the tank was full. When I looked closer, I noticed that the main bolt anchoring the gas tank was only finger tight. Grrr.
I tightened it up and all was back to normal.
I have always had a slight increase in buzz that starts at about 5K rpm. As I recall it calmed down above 6K or so, but now it seems to carry through all the way to redline. Back in the beginning, I figured that it was simply from the factory crash bars combined with the EG skid plate and that I was stuck with it. It wasn't overly irritating, but it is enough to blur the rear view mirror images. Biggest trouble is that the speed limits here are 80 mph which puts the Vee2 in 6th gear right at 5K rpm. So there is the potential for cruising hours at a time in the buzziest rpm range.
I've been reading a bunch of vibration threads lately and have contemplated revisiting the issue. My bike is technically due for the "Throttle Body " sync per the owner's manual maintenance schedule, which requires the dealer diagnostic tool to perform. However, at least for the Vee2, that only really balances the idle circuit by setting the idle air control valves (needs the dealer diagnostic tool to put it into a mode where they stay put and won't try to automatically compensate). This should have little to no effect on partial throttle running at 5K rpm on the freeway. My bike is a bit rough when cold, below 3K rpm, and barely cracked throttle; which I would expect to get much better after completing the sync procedure since that is right in the realm of the IAC valves' control.
Dmfdmf posted here
about the actual throttle body butterfly valves being synced a the factory (at least for the 650's). I have looked through the Vee2 service manual and it also does not have a procedure for correcting butterfly valve sync. I have to wonder if it would be possible to sync them DIY style. There are devices out there that are used for syncing carbs on in-lines as well as any other setup that uses more than one carb. Could one of those be used to sync, or at least measure the sync of the butterfly valves on these bikes?
The various attachments like crash bars, skid plates, etc. can change the harmonics and amplify the vibrations at resonant frequencies, but if I can find and correct the source of the vibration (as dmfdmf mentioned, likely an imbalance of power between the two cylinders), then the resonance and harmonics wouldn't have as much of a source "wave" to work with.
One of these days, I'll have to do some centerstand poking and listening to try to identify which parts are involved. Although, it is entirely possible that it is running just fine and won't get much less vibration. It is very subjective and difficult to quantify through text alone on the internet...