There was a guy that "over balanced" quadra engines some years back. His name was Dario B????? My cousin sent his quadra to this guy and it came back super smooth. I am not sure how he did this. I am guessing he had a theory to have the flywheel out of balance in a cetain posistion relitive to the rod/piston posistion. Just a guess. I wish someone who knows how Dario did his magic, would shed some imfo on the subject of balancing. Thanks Capt,n