engine overrevving

[corvettealbert68]

I recently bought a 1993 wellcraft 23.6 walkaround with a merc 2.5 200hp out board.
Day one after running the boat for about 2 hours the engine started over reving or cavitating i tryed to make it back little by little was eventally towed back. The prop was spun and so i had it rebushed went out again, and again after 2 hours the problem started again. I had someone check and rebalance the prop checked the shifter cable and now it seems to come out of gear and started over reving anytime after 2000rpms.
And so i went as far as replacing the lower unit thinking the dog gear was wore but still the problem cotinues with a new lower unit and a re-balanced and re bushed prop. I lost please help.
Thanks Al.

 

[bullbat]

Re: engine overrevving

do you have the linkage adjusted right and allowing it to go all the way in gear

 

[CharlieB]

Re: engine overrevving

Check the water pump housing for heat damage.

When you changed lowers did you also change the water pump?

Some motors developed a problem with excessive exhaust heat damaging prop hubs, make SURE that your water pump is in good shape and that there is not a 'grove' worn into the stainless parts from the raised ring on the sides of the impeller.

Verify ignition timing is correct, carb jets clean.

Worst case, some have drilled a 1/16th hole into the water transfer tube to spill water into the exhaust to aid cooling exhaust gases.