Everybike produces vibrations from the engine its just the XT being a big single makes alot more than most bikes. As youve said you have already tried heavier bar end weights why not try a heavier bar itself, fill the bars with sand, change the gearing, buy foam grips etc etc.

There are a few options to try but mostly they will dampen the vibration but not totally make it dissapear. I dont think anyone have found a solution to totally make the vibration go away yet.

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Plough on