There is a procedure in the repair manual. I don't remember it off the top of my head, but you verify synchronization of the carb linkages by verifying that they all open at the exact same moment, and butterflies are fully opened at the same time. You verify synchronization of the throttle by making sure the roller is hitting the throttle cam on the mark that is scribed on the throttle cam. Again, the exact measurements and procedure is in the repair manual.How do you verifie carburetor synchronization?