We have a 1999 Mercury 40H 4 stroke 747 cc. Had 1 carb replaced & 2 carb kits recently replaced. The tech said it didn't run at top rpm. So he ordered us a 12.5 X 8 prop. At idol vibration is bad. Kick it in a bit & it smooths out. Original prop was 12 X 10.5 & it labors a touch. We have it on...
