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.

__________________