I have ridden more vertical twins than I can count.I own 20 personally and work on at least another 20 for people on a regular basis. Every one has a vibration to it. If it is a mild vibration you are probably just feeling the nature of the beast. If it is a bad vibration there are many possibilities ranging from tire wear or wheel true to carb sync. to internal problem. From what you describe I believe it to be the former , ie normal.

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