It sounds to me like the ring on the flywheel is too far rearward, on a top starter motor, the ring gear gets moved toward the rear of the flywheel.
The flywheel would need to be removed and the ring heated up and flipped around and reinstalled back on the flywheel toward the front edge.
You could test this theory by removing the bendix shims from the starter and see if it improves, but it will not fix it, it will only get better.
I would pull the motor loose and set it on blocks in the boat and remove the flywheel and check it out. You can leave the motor hooked to fuel and electrical so you can test it before getting everything back together..
Hope this helps you get closer...
U think i should just buy flex plate?
Sent from my PantechP9070 using SoCal Jet Boats mobile app
No... I don't.
GT