'88 100hp cavitation? prop spline gear?

[beckoning]

'88 100hp, 4 cyl oil injection. For no apparent reason today, while cruising at 3,500 rpm, the engine raced as if it came out of gear. I checked the prop for damage (cavitation?) and it was clean, even though it is an old prop. Nothing has changed on the boat to cause interference to the water flow under the boat to the prop. I haven't removed the prop yet. Could it be the rubber spline gear on the prop has worn so the spline gear and shaft engage at slow speed, but over 2,000 rpm the propeller shaft just spins inside the prop? It seems to be rapidly getting worse as if the rubber spline gear is quickly wearing off.

If the spline gear is the problem, can I replace the rubber spline gear on the prop? Or is the best approach to replace the prop and spline?

 

[MH Hawker]

actually the older props have a press in rubber sleeve in between the drive spline shaft and the prop and after time it starts to slip, and your description is a classic description the easy is to mark a line on it and give it a ride and let it slip at least once then pull it out and inspect


and yes you can have a new sleeve pressed in

 

[beckoning]

Hawker, Thanks. My local prop repair guru pressed out the old and pressed in a new insides, including a new brass spline and rubber sleeve, and trued up the prop angle. Runs like a champ. Now my problem is my 2010 Merc 9.9 4cycle kicker seems to run fine for a while, then seems to load up and start running on one cylinder. If I rev it up, it finally clears. Could it be a bad plug, maybe water in the gas. Don't know if it has carb(s) or EFI. If carbs, can I drain the bowls?