With bar-type blades, I generally balance them by hanging them on a nail driven into a tree beside the shed.
After sharpening (particularly if I've had to grind a bit off the blade as a result of someone using it for a laser-leveller) I hang the blade on the nail to see if one side is consistently heavier than the other. Judicious use of the grinder on the offending side until the blade balances is usually enough to prevent any unwanted vibration.
I have never had any problem running a B&S without the blades (just watch the revs - they can climb really fast without the inertia of the blade to ease them up a bit).
