Help with over revving. 1985 (86) 25 hp evinrude

[Fishahollik]

This is a 1985 or 86 25 Hp evinrude thru hub exhaust motor without shear pins mounted on a 16' flat bottom. I recently had the boat out and ran into a sandbar going a little over idle speed. I held the motor up to keep prop out of the sand until water was deep again. Began to accelerate to full throttle and engine would over rev like the prop is cavitating. I slowed down, checked for weeds, debris etc... Prop is clean. I assumed spun hub on prop. I changed to a spare prop, same thing happened. Could both hubs be spun? Possible but unlikely. What else could cause this?

 

[flyingscott]

Draw a line across the hub and see if it moves when you run it.

 

[Newyota]

Were you in heavy waves?I have an 85' 20hp that I bought last year and got caught in heavy waves right after I got it in my 14' jon and had to slow, and when I did try to increase speed it would rev high.Thought I bought a lemon!Waves were coming into the bow and rolling under me and I believe was causing it to cavitate or there may be another name for what was happening.Never happened since.

 

[Fishahollik]

No waves, nearly dead calm. Both props didi the same thing, no noises, just over rev when trying to go to WOT. As it stands right now, it seems its either gears or prop, a new prop is the cheaper route. Have not been able to get boat in water again to try marking the HUB.

 

[Newyota]

I have seen where the teeth on the clutch dog and gears have been re-cut if they are rounded and are not engaging.May be an option?Possible your shift rod needs adjusted only or something there came loose?Check that before buying anything.

 

[Chinewalker]

Drain your lower unit oil, looking for shiny bits. If there's metal in there, you may have spun your pinion...

 

[oldboat1]

^^^think that's right. Guessing the prop probably caught a sandbar at maybe 800 to 1000 rpm, which could do some gear damage. (And maybe you understated speed a bit...)

I sometimes do battle with gravel. Not sure what's worse, but probably doesn't matter much. I miss shear pins.