RPMs out of control

[Frosty Buds]

I have a 15hp yamaha tiller (15FMH) I
I hit something at full throttle around 35mph, the engine took a really hard hit, I was thrown from the boat but managed to get a handhold on the transom and pull the kill rope that i wasn't wearing

The engine appears fine on the outside but now its rpms go up and down on its own. I have to keep adjusting the throttle to keep them steady. It idles fine and runs perfect at low speeds but bogs down when at full throttle. Also it won't shift into reverse now when I pull the foot down a bit it will go in but messes up again when I bolt it back on.

So rpms all over the place when on plane
Bogs down at full throttle from a standstill
won't go into reverse unless foot is pulled down
Thanks in advance for any suggestions

 

[dwco5051]

How badly was the prop damaged or did the lower unit take the full impact? You said it looks fine from the outside but did you check where the upper part of the intermediate unit bolts to the motor?

 

[Frosty Buds]

The prop wasn't damaged discerningly the gearbox took the full impact i guess. Didn't find any loose bolts anywhere thankfully.

 

[Frosty Buds]

Took the boat out yesterday and she gets up on plane if I apply slow steady gas then seems to over throttle. Seems way faster than before the crash and the rpms fluctuate sometimes from half throttle to full. No fluctuation near idle speed. Im gonna check cylinder compression and try a carb rebuild next I guess.

 

[dwco5051]

Have you checked the prop yet for a possible spun hub?

 

[99yam40]

Took the boat out yesterday and she gets up on plane if I apply slow steady gas then seems to over throttle. Seems way faster than before the crash and the rpms fluctuate sometimes from half throttle to full. No fluctuation near idle speed. Im gonna check cylinder compression and try a carb rebuild next I guess.

what do you mean it seems way faster now?
boat moves faster across the water?
or just motor RPMs seem higher when it revs up sometimes while under a load?

these Yamaha's are normally spring loaded into forward, and have to compress the spring to go to neutral and reverse.

you need to find out what has happened to the linkage .
something bent or twisted maybe