1975 25 HP model no. 25R75B Johnson outboard

[Herbty]

Overall it runs great but, at high speeds the engine will run good for a short period and then revs up and acts as if it was put back in the neutral position.
Any ideas what might be causing outboard to do that?

Thanks,

 

[Will Bark]

Re: 1975 25 HP model no. 25R75B Johnson outboard

Sounds like a "spun" prop hub; mark a line on the hub and prop then run it till it slips, see if the lines are still lined up. If not then you need to get prop re-hubbed at a prop repair shop. Good luck.

 

[AEROCOOK]

Re: 1975 25 HP model no. 25R75B Johnson outboard

Worn out clutch dog.

 

[steelespike]

Re: 1975 25 HP model no. 25R75B Johnson outboard

If its the Clutch dog it will clunk like you hit something.

 

[Herbty]

Re: 1975 25 HP model no. 25R75B Johnson outboard

Thank you very much for your help. Out on the lake we did hear a clunk and yes we thought we hit a piece of wood. Two other questions. I'm looking at a parts list, is there another name for the clutch dog? When I take it apart what type of condition would be considered good for the clutch dog?

Thanks,

 

[Herbty]

Re: 1975 25 HP model no. 25R75B Johnson outboard

I did find the clutch dog on the parts list.

 

[dockrat100]

Re: 1975 25 HP model no. 25R75B Johnson outboard

Look for rounded edges on the engaging surfaces. Also check for rounded edges on the gears engaging surfaces.

 

[Toughlife200700]

Re: 1975 25 HP model no. 25R75B Johnson outboard

the question is does it clunk every time it reves up like that. that would be the clutch dog. if it only done it the first time then you might have hit something knocking the hub loose from the prop. if it just reves up now and doesnt clunk then it needs to be rehubbed. if it does clunk every time you need the clutch dog. I dont know if most people agree or not but when i pulled my foot apart to replace a clutch dog i replaced the whole gear set. i figured if i was going that deep in the foot id just take care of all current and future problems at once..

 

[steelespike]

Re: 1975 25 HP model no. 25R75B Johnson outboard

Good point if its a worn dog it will clunk every time.
There are also 2 detent balls and a spring that helps keep the dog in-gauged.Be sure they are present and don't lose them.

 

[Herbty]

Re: 1975 25 HP model no. 25R75B Johnson outboard

1975 25 HP model no. 25R75B Johnson outboard
It overheated :grumpy:

 

[Herbty]

Re: 1975 25 HP model no. 25R75B Johnson outboard

Update - After it overheated I replaced the head gasket, thermostat and thermostat housing gasket. It's running good now but, it still slips out of gear at high speeds. Clutch dog looks good not worn (I took it down to the boat shop to have them take a look). I disconnected the throttle and shift cables and it still pops out at high rpm's.