Twin 150 Yamaha sync question.

[jasoncooperpcola]

On my 250 Sportsman both engines seem to keep up with each other until about 3000 rpm. After that the starboard engine has to be advanced more to keep up. With the shift handle all the way down it only turns 4500 rpm. The port engine still has lots of throttle left. The only way i can think of getting them in sync with each other is to extend the starboard engines throttle cable at the end more. It looks like all i have to do is take it loose from the motor and turn it to lengthen it. Is that the only way or is there another way. At 4500 rpm the boat was running 45 mph. Also the max rpm range (according to the book) is 5000-5500 rpm. What kind of speed san i expect with both engines turning 55000 rpm?