If the blades are off enough to prevent the shafts from running true, they knock the flybar out of true at speed. The shake of a heli can prevent the flybar from doing it's job. Some balance blades and some don't, but the more true the heli runs, the better it all works. Perfection is not required. If it's got a bad shake, that will bind the flybar at the rpm the rotor spins when it flies.

If you can't get the rotors to track even though they are balanced, they may be warped. Search for warped rotors on the forum. We have been boiling them for 5 minutes to get them to return to the original shape.

Good luck.
Soloboss