There should be two stop screws, one for forward and one for backward travel of the lever on the mechanism under the helm deck in addition to the adjustment on the other end of the cable at the carb. I'd start by checking the stops at the helm to see if they are in sync and if so, adjust the length of the cables at the carbs. The stops play an important role by preventing the cable from stretching over time. Between adjusting the stops and the length, you should be able to twin up the two levers. Its an iterative process.
Whitney,
There should be two stop screws, one for forward and one for backward travel of the lever on the mechanism under the helm deck in addition to the adjustment on the other end of the cable at the carb. I'd start by checking the stops at the helm to see if they are in sync and if so, adjust the length of the cables at the carbs. The stops play an important role by preventing the cable from stretching over time. Between adjusting the stops and the length, you should be able to twin up the two levers. Its an iterative process.