Marine Mechanic-115 Merc 4 Stroke

[Huskie]

My 115 merc 4 stroke (2006) is acting up.  At about 2/3 throttle, 30 mph, 4000 rpm's the motor seems to cavitate or rev up and the tach pops way up, but we didn't speed up.  I quickly backed off and ran at a lower speed.  I have it trimmed up on plane but not overly so.  It did it once at a lower speed as well.  Most of the time at lower speeds it riund fine. Brought it in and they looked at it and pulled the prop and everything looked fine there etc.  The motors lower plate seems to be located correctly, right at the bottom of the boat.  Going on one last trip, and don't really have much time to bring it in for an extensive diagnosis, might need to baby it and stay close to the landing.  Any ideas?

[spoonsncranks]

The rubber insert in the prop may be spinning at higher speeds. It's worth it to try a new one, relatively inexpensive.

[Borch]

99% sure is the plastic exhaust ring that snaps into the hub in front of the prop.  Had the same issue and 2 trips to the dealer to get it figured out.  Silicone the new one in and pick up a spare.   The difference is night and day.

 

Could be a bad rubber hub but I doubt it based on your description of the issue.

[Huskie]

thanks for the response, will take a look at those solutions.