What's the best upgrade to reduce vibration on the 919 handlebars? Renthal Bars or the 17/44 gears? Everything is still stock on my 919 and I'm getting tired of the numb hands! Eventually I would like to do both.
Renthal bars first with a set of bar end weights. Far cheaper and it might just be all you need to do. Wait until it's chain replacement time before doing that. I did both (Renthal plus 17/44) as well as Vibranator inserts. Every little bit helps.
You can sync the enrichers but not the throttle bodies, I believe. Which will do nothing for vibes.
Now sync'ing the throttle bodies does make a difference. In fact, it was night and day difference on my SV1000.