Having problems with motor

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txneal

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Location
Alpine, Texas
I just spent two days on the lake and experienced some trouble with my motor, so I'm hoping that some of you guys might be able to help me figure out what I need to look for. The motor is a 1973 Evinrude 25hp with tiller. It runs really great most of the time, but every so often it just seems to suddenly rev up the rpm real high and the prop quits turning. Over a period of two days on the lake, it happened to me about 5 times. It only seems to happen when I am cruising at wot. I'll just be going along just fine and then it will suddenly happen. I can let off the throttle and then it will catch and start turning again. It will run perfectly for a while and then it will happen again! Its as if it just momentarily jumps out of gear and then when I let off the throttle, it goes back into gear. It only happened about 5 times over a period of two full days on the lake, but I'm pretty concerned about what it is and want to find the cause and fix it before I take the boat out again.

If any of you guys have some suggestions for something that might be causing this or anything that I might try to correct it, I would really appreciate the assistance. This has never happened to me with this motor in the past, but I was carrying more weight this time than what I have ever carried before. It is a 14 foot semi-v starcraft and I had a guy up front and then about 20 gallons of water in a bait tank toward the rear/center of the boat, and also a bunch of fishing gear.. I thought that maybe the extra weight might have something to do with it, but I have no idea what it is.
 
Sounds like it may have spun the rubber hub in the prop. Relatively cheap fix at the prop shop. Also, if you have had the prop off for any reason might check to see that the prop nut is torqued down properly.
 
Definitely check the shear pin, I'll bet it is sheared. Also, you may be ventilating, but this is less likely. If it hasn't happened before, and you have made no changes, then it shouldn't be ventilating; more weight would not make it ventilate. However, if you have moved to motor up on the transom or you are in a higher trim/tilt hole it could.
 
exact same problem I had with my 20hp johnson...

Changed the prop and it solved everything.. the rubber hub in the prop is shot
 
Thanks for all of the replies so far. I'm glad to hear that it may just be in need of prop attention because I was getting worried that there might be something more serious going on in the lower end. I'm at work right now, so I can't look at it until I get home this afternoon, but I'll definitely pull the prop and check it out. That is the only prop I have and it is ancient and a little dinged up, so I've been planning to purchase a new prop anyway. This could certainly be the motivation I need to get it ordered. So If the pin was sheared or the rubber hub is spun, it could still turn most of the time and just slip occasionally? Yesterday morning, I ran it for about half an hour and it slipped twice during that time. Then, I went a few of miles up the Colorado River and was facing a strong headwind and some significant waves and it just pushed along with no trouble at all.
 
Sorry to be the one who does not beleive this is your prop hub but I don't. I've spun many props and have never had one that works most of the time under a load and only free spins once in a great while. Mine all worked at only idle speeds and free spun under any load when it was the prop. I went through 6 props on my last boat due to the harsh lake we love so much... :twisted: Any ways I really hope you prove me wrong on this one. Now as for the shear pin, I have never had that problem, so maybe its that. Best of luck man.
 
Well, perchin, I was wondering how it could be working most of the time and just slipping occasionally if it is a spun hub or sheared pin. My thinking was that if it was a pin, it would just spin free all the time and not be working at all. Then again, I haven't ever experienced this before, so I don't know what to think about it. If it turns out that it isn't a problem with the propeller, then where should I focus my attention next?
 
For now let's just [-o< that it is indeed the hub, or shear pin. I don't know much more about the inside workings of an lower end on an outboard. I'm sure someone who does though will be able to help if need be.
 
When you are getting up to WOT, you get going then all of a sudden the motor just revs up, you slow down, let off the throttle and it starts back up again - and then it will do it again about 5-10 seconds later... usually only happens when you are wide open, or when you are on your way to full throttle. Happened to me nearly every time I was out. Some days it wouldn't do it at all, sometimes only once.

It's funny man, but I know exactly what you are dealing with. I had an OLD prop on mine too.. when I took it to my repair guy he told me he thought it was the hub, but wouldn't know until he got into it. When I got there, he had the new prop on and said the hub was jacked up and would catch and wedge itself, that's why it would run sometimes and not others.

Props are about $100 and comes with the hub... go ahead and spend the dough - and wait til you see how much better your engine runs after that. I couldn't believe the difference
 
Russ: from what you describe, you were experiencing exactly what is happening with mine. Since I planned to get a new prop anyway, I'm going to give that a try. If I take the prop off and look at the hub, should I be able to tell that there is something wrong with it?
 
I have no idea man... I had the repair guy fix mine so I have no idea what it looks like in there.

I can work on car engines, but you couldn't pay me to touch a marine motor - that's why I let him fix it while he was tuning it up. Since it's a rubber hub, I would think you would be able to see if it's torn or something like that
 
You should be able to see if the rubber hub has become seperated from the prop with a spun prop, although the last one I spun was only 2 weeks old and I couldn't see any damage to the rubber, but it was indeed spun.
 
You won't be able to tell just by looking at it.

You can even drive the hub out of the prop and still not be able to tell unless it has galled the rubber.
 
Quackrstackr said:
You won't be able to tell just by looking at it.

You can even drive the hub out of the prop and still not be able to tell unless it has galled the rubber.

huh???? 5 out of 6 I could visibly tell without question that they were spun. As in black streaks on the inside edge of the aluminum from the hub spinning in the prop. Also from the little erasor like shavings it seemed to of caused, not to mention the rubber being a lil messed up around the edges.

you should also Remove the propeller from the propeller shaft. Inspect the rear bearing surface of the propeller for circumferential scratches indicating the propeller has been turning at a different speed than the propeller shaft/thrust bearing.
 
I guess it depends on the prop design.

I've got 2 of them at the house right now (Evinrude) that are spun that you wouldn't know unless I told you. You can't even see the rubber in them, much less black streaks.
 
well, I just got home and pulled the prop and I can't see any damage at all. It sure couldn't hurt anything to have a new prop, so I'm going to order one and hope that it will fix the problem. I appreciate the help you guys have given me. At least I now have hope that a new prop will fix it and that maybe there's nothing wrong in the lower unit. It might be a while before I know for sure because I'm getting ready to leave for Germany and won't be back for a month. I guess I'll have a new prop to go test out when I get back!
 
txneal said:
well, I just got home and pulled the prop and I can't see any damage at all. It sure couldn't hurt anything to have a new prop, so I'm going to order one and hope that it will fix the problem. I appreciate the help you guys have given me. At least I now have hope that a new prop will fix it and that maybe there's nothing wrong in the lower unit. It might be a while before I know for sure because I'm getting ready to leave for Germany and won't be back for a month. I guess I'll have a new prop to go test out when I get back!

A new prop is never a bad idea. Keep the old one in the boat. One day, when you find the shallowest rock in the lake at WOT, you'll be glad you have the spare. You can idle back to the dock with a spun prop a lot better than you can make it back with a prop lacking all 3 blades.
 
Keep us posted and let us know what happens when you put on a new prop. I have a 35 hp Johnson doing the same thing, I have just acquired a extra prop and will give it a try in the next few days. Somewhere on this forum I have read about a motor doing the same thing and it being a worn clutch dog, which engages the gears and then pops out at WOT causing the same symptoms.
I have spun a hub before on another motor and after it was spun, it always spun on me at WOT. If the prop does not fix both our motors we may have to search out more info on the clutch dog. Keeping my fingers crossed.

Flintcreek
 
flintcreek: I'm just finishing up a job and will be too busy to get to the water before I leave for Germany, so it will be about 6 weeks before I can go test out a new prop. There is the slightest possibilty that I might be able to get a prop and run up to the lake before I leave, but it is unlikely. In the meantime, I'll be very interested in knowing if the new prop has corrected your problem, so please post back here as soon as you have given it a try. A worn clutch dog sounds like way more work than replacing a propeller , so I've got my fingers crossed on this one.
 

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