Vibes won't go away through tightening the mounts, they need to be done up tight, no matter what. They are not pre-tensioned in any way, the vibration isolation is through the rubber inserts, not their mounts.
Check the carb synch, especially the play in the individual linkage shafts.
Depending on your ignition system, check timing on ALL cylinders, a pick-up may have the polarity reversed and will thus fire way off from where it should. If that is the case, you should have experienced other, more severe damage by now!
Check all rubber mounts, when one goes soft it can influence the others to the degree that they get pummelled and one after the other is pulverised.
If all is well, you may have the same problem as I do..... I'm tipping on an out of phase crank!
piet