Is it advisable to "upgrade" to a lightened crank pulley?

[Def]

Originally Posted by UNISA JECS

The best thing you can do is make sure the pulley is balanced if its a lightened aftermarket pulley, to me the lighter the less effect teh pulley shoudl have on harmonics if it is balanced. But between the KA and SR, the SR should be better suited to deal with harmonics because the crankshaft is fully counterweighted whereas the KA is only half counterweighted.

Lightness has nothing to do with it. This vibration is a result of an imbalance in the rotating assembly, it's the crank's natural frequency when being subjected to power strokes. Just like a tuning fork vibrates, so will your crank when excited at this natural frequency.