I may be going off topic a little here but on my first 660z I noticed vibrations increased when I fitted the Yamaha engine bars. It's possible vibrations worsen when various types of engine/crash bars are fitted and the engine vibes are transmitted via the bars to the frame/seat/footpegs/handlebars.

Not sure how having a full or empty fuel tank will change the amount of vibes though.

(the original Yamaha brs cracked,, changed themunder warranty and the second set cracked)

A lot of people complain of vibrations increasing after recently fitting engine bars. Quite often it is because the engine mounting bolts have been disturbed to fit them and not always re-torqued carefully enough. Too tight and too loose can cause more vibes - the mounts need to be spot on.

A full tank will tend to increase vibrations at certain engine speeds simply because it's a bigger weight to move, so it doesn't soak up/absorb so much of the vibrations. In other words it's resonant frequency will change. Fitting crash bars, or anything else for that matter will have a similar effect. They won't necessarily get rid of, or increase vibrations they'll just mask them, or amplify them at different frequencies. Same principle behind bar-end weights.

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