# Early 70's 25hp Johnson revs up and loses power



## eric.schimmel (May 7, 2015)

Hey everyone, 

I've stalked these forums for a long time but have never taken the opportunity to post. First off I'll start with a little about the boat. It's a mid 50's ouachita 1448. I recently upgraded the 7.5hp Johnson I had for an early 70's Johnson 25hp. It runs fine most of the time but I have been having an issue sometimes while running at speed. It'll get up and go, usually cruising about 22-23mph then out of no where the rpms sound like they skyrocket and it loses power and runs about 14mph. If I slow down a few times it tends to fix the issue but this last time out, it was happening more often than I would like. I took a video of it and I'm hoping you can help. Also, the carb, fuel pump and impeller have all been rebuilt. I thought it might be cavitation but the cavitation plate sits level with the bottom of the boat and it has a hydrofoil so I'm pretty sure it's not the issue. 

https://youtu.be/mLiollcmu1I

Any help you could give me would be greatly appreciated. Thanks!


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## ggoldy (May 7, 2015)

Slipping prop?


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## eric.schimmel (May 7, 2015)

That was one of the other thoughts that I had but I don't know the symptoms of a slipping prop or what to look for.


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## eric.schimmel (May 8, 2015)

Well I took the opportunity today to drain the gear oil. I'm fairly new to boat motors but I'm pretty positive this is not what the gear oil should look like...


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## KillerJ (May 8, 2015)

No, that is a definite water/gear oil slurry.


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## KMixson (May 8, 2015)

Spun prop? The spline portion of your prop has a rubber interface between it and the actual prop. The rubber portion breaks and the prop is then able to spin around the spline mounted on the output shaft. At low speeds the resistance was enough to turn the prop until it hit its break loose point. Then the engine revs up but the prop does not turn as fast as the output shaft turns. The more it happens the worse it is going to get. If you over rev the the output shaft you may damage the shaft seal and then water will get into your lower unit. You should not be able to spin your prop on the inner splined portion by hand. The rubber is there in case you hit something with your prop to break the rubber interface before it damages your motor or lower unit too badly.


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## eric.schimmel (May 8, 2015)

Well that sounds exactly like the issue I'm having. So what is the fix for a spun prop? Is my only option to replace the prop?


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## KMixson (May 8, 2015)

Myself, I would replace the prop. You might as well replace the seals in the lower unit while you are there.


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## eric.schimmel (May 8, 2015)

Could anyone tell me which seals I would need for the prop shaft and any other seals that may have caused the mixture of water in the gear case?


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## jasper60103 (May 9, 2015)

eric.schimmel said:


> Could anyone tell me which seals I would need for the prop shaft and any other seals that may have caused the mixture of water in the gear case?



The drain/fill plug seals are the usual first suspects. 
Replace those first and refill. 
If that doesn't work, you
can buy a complete lower unit seal kit from your local dealer or iBoats.
Good luck.

https://www.iboats.com/Johnson-Lower-Unit-Seal-Kits/dm/cart_id.447586306--session_id.715175949--view_id.271288


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## eric.schimmel (May 9, 2015)

Awesome. Thank you. Looks like I'll be ordering that and a new prop in the very near future. Thanks for all the help!


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## Boat2fast (May 10, 2015)

Sounds to me like a spun prop too. Spun a few myself on those motors. Careful not to over-prop those 25s. They turn 1000 rpm higher than the 18s to make their power. Check Max operating range. Now put a tach on your engine. Full speed rpm should be right near the top of the range.

The shift shaft seal is easier to change with the factory tool. Sometimes the dealer has an advantage here. Ask him to install the seal for you.


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## restornator (May 10, 2015)

for the shift shaft seal, I use an extended flat wood drill bit. cut the business end off so you can tap on it.


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## eric.schimmel (Jun 30, 2015)

Hey everyone. It's been a few months and I got the opportunity to replace the prop and the seals but I'm having yet another issue with this motor now. It seems like when I'm under speed it's popping out of gear and back in. Almost like a little surge. So I pulled the bottom end back apart to inspect the clutch dog and gears. I don't see any sign of wear on either. Could the clutch dog go bad without showing signs? Any help you could give me would be greatly appreciated!


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## Pappy (Jun 30, 2015)

There is an adjustment to make sure the lower unit is fully into gear. However, at this point, the clutch dog is probably rounded. 
The short time cure for that is to reverse the clutch dog on the propshaft.
Hint......if you are thinking of taking a short cut here and just doing the adjustment outlined below and the clutch dog slips again, chances are you will have a non usable clutch dog and forward gear. At this point you may have that condition already. The adjustment below is assuming you have fully serviceable parts. 
Now, at your shift lever, look at the way the lever is mounted and you will see a slotted bracket behind the lever. Loosen the pinch bolt on the lever and the bolt on the slotted shaft assembly. You will essentially be moving the lever backward a little bit on the slotted bracket. This will force the shift shaft to locate the clutch dog all the way into forward gear. 
How do you know when it is correct? 
With the prop on the shaft, get a "feel" for the rotational resistance in neutral. Then shift the unit into forward gear.....feel a difference? No? Then the clutch dog is not bottomed out in forward gear yet. 
Physically pull the shift lever farther than it is supposed to go in forward gear position. Feel a difference now? If so, that increase in rotational drag is what you are looking for when you make your adjustment. 
Re-adjust in small increments until you feel that increase in drag and you are properly adjusted.


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## eric.schimmel (Jun 30, 2015)

As soon as I get home I'll make the adjustments you mentioned and see if that helps. In the meantime, here is a video I took of it. I'm sure that is what it is because I was watching the shift lever and I could see it starting to move backwards before it surged. 

https://youtu.be/jWfqRoUYNhY


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## eric.schimmel (Jun 30, 2015)

Ok, so I pulled the shift lever off to clean it up a bit and inspect the parts and what I found is the little plastic piece on the backside of the lever that seats inside the slotted bracket looks very worn out. Is it possible that this is the culprit for causing it to slip out of gear?


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## Pappy (Jun 30, 2015)

That is a factor but not the culprit. Replace the bushing by all means.
If you read the post again...the push was to get you to open up the gearcase and turn the clutch dog around before doing the adjustment. 
You can see if you have anything to work with before you adjust.


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## eric.schimmel (Jul 1, 2015)

Pictures keep posting in wrong order.


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## eric.schimmel (Jul 1, 2015)

Ok, so I pulled the bottom end off again and noticed I do have a lot more wear than I ever noticed. I'm pretty sure I'm going to be rebuilding the bottom end. I'm not sure who rebuilt this for the previous owner or if he did it himself but I was missing a ball bearing for the clutch dog; issue 1. Secondly one of the thrust washers was seized to the shaft. Took a bit of work to get that off. Second the clutch dog and the little arm for it show significant signs of wear. 

This is the side of the clutch dog with the seized thrust washer (reverse side). Is that groove normal? The diameter of the washer is too large for the groove. 



Forward side. Some rounding. No groove. 



This is the bracket for the clutch dog. Some signs of wear. Replace?



And finally, the forward gear.


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