81 Johnson Help

Ive got an 81 Johnson Tiller steer and Im having a problem and am a real novice as far as outboard motors go so Ill explain as best I can and hopefully someone will understand.

When running the motor at around mid range the motor sounds as if it either kicks out of gear or goes into overdrive,when you get on plane it actually rund pretty good but will still do it at top range just not as bad.When it makes the noise and you also feel a lag/the boat drops as if again it feels like its kicked out of gear or went into overdrive or something

I am running the motor on a Seaark 1652 Tunnel hull.

I had a buddy out duckin this morning and we were kicking around the idea of maybe its not drawing enough water,its not peeing hard but its steady,plus there seems to be a second pee hole in the front?

I had the lower unit serviced and the pump changed,but it was doing this before and after the service work?

Also thinking it could be a prop problem I tried pulling off the prop to see if the splines were damaged as it obviously stops or studders (the prop that is) when it makes this sound.But couldnt get the prop off,I pulled out the cotter pin and took off the nut is there something Im missing,I couldnt even pound it off with a rubber mallett

Sorry for the long post but I desperately need some help/ideas!

Thanks in advance.
Chris

Re: 81 Johnson Help

81 Johnson Tiller WHAT?

Re: 81 Johnson Help

Sorry

1981 johnson seahorse tiller steer outboard

25 hp

Model J25rlcim.....Pretty sure the last is an "M" kinda hard to read on the plate

Re: 81 Johnson Help

1. When did this problem start?
2. Is the motor new to you?
3. Did the problem start after the water pump change?
4. DId you get the impeller only changed or the impeller and pump housing?

5. What does the water pump indicator stream look like on idle?
6. Is it nice and straight when it comes out until it hits the water on fast idle? It should. If not, check for an obstruction in the hose or the nipple that it exits out of.
7. How does the cylinder head feel after you run it for a decent distance? You should be able to hold your finger on it for 3 seconds without it burning you. If you can't hold it on there that long, it's overheating.

However, the water pump doesn't have anything to do with your problem. It sounds like it could be a bad clutch dog in the lower unit or a misadjusted shifter.
8. Does it feel like you hit a small stump and then over-revs? Or does it just kind of suddenly over-rev and lose power? IF the stump thing, it's probably a clutch dog or misadjusted shifter. If the other, then probably a slipping prop.

Sorry for all the questions but the more you know, the easier it is to tell what the problem might be.
9. Also, what did that "lower unit service" consist of? An oil change or a disassembly/reassembly with new parts?
It is odd that you just had the lower unit serviced and can't get the prop off. I would think that a lower unit service would at least consist of changing the oil and removing the prop to check for fishing line and greasing the prop shaft splines.
Got any more info?
good luck,
JBJ

Re: 81 Johnson Help

Ill try to answer the best I can but keep in mind my greenness as far as boats/motors go:redface:
1.As long as I have owned it
2.Yes new to me
3.Before and after
4.I believe just the impeller
5. at idle it just kind of sprays noy hard but more than a drip
6.not really,I went out and looked at it and it seems the hose to the nipple may be brittle and dry rotted,is this a replacement part,it seems to have a fitting on one end as opposed to just being able to pick up a piece of hose
7.Havent tried the cylinder head/heat thing but it doesnt seem as if its running hot.....
8.It feels as if it just kind of over revs so from what you have said it sounds more like a slipping prop,the prop seems to be in pretty rough shape and needs to be replaced any way,any tips on getting it off,and if it is slipping what should I look for,and will I have to replace anything other than the prop to solve the problem
9. as far as the lower unit service he disasembled it changed the water pump and oil,I had actually taken the motor in for some choke/carb work and this was an after thought.But I know he disasembled it because he actually broke one of the housings and had to replace it.

Thanks and I look foreward to your reply!

Re: 81 Johnson Help

I would replace the prop first then test run it. If the mechanic had the lower unit apart then he should have greased the splines on the prop shaft.
If you have the prop nut off then it should slide off very easy.
Hopefully you get the prop off and it was just the prop hub slipping.

Re: 81 Johnson Help

It could be cavitating. Duck hunting gets you into weeds, right? Weeds cause cavitation.

Re: 81 Johnson Help

F_R said:

It could be cavitating. Duck hunting gets you into weeds, right? Weeds cause cavitation.

Click to expand...

No weeds I was in the middle of the river but how do you fix/cure cavitation?
At this point Im almost thinking its the prop hub slipping,just gotta get it off somehow

Re: 81 Johnson Help

If it were me, I'd take it to the mechanic who rebuilt your lower unit and ask him to take the prop off. That way, if he breaks anything getting it off it will be his own fault. I don't have any tips on how to do it but suggest you don't pry on the housing in any way. It's made of brittle aluminum metal and will break if you try!
GOod luck,
JBJ

Re: 81 Johnson Help

You seem to indicate that it is worse at mid range than at top speed. That makes me doubt the spun prop hub theory. With a spun hub, the more power you apply, the worse it gets.

I still suspect cavitation. Probably something inherent with the setup. Especially considering it is a tunnel hull.

Cavitation is caused by anything that causes air bubbles to get around the propeller. That includes too-high mounting or something wierd about the boat hull.

HOWEVER, there is a second consideration: The noise, stuttering, and whatever. Noise and grinding is not a characteristic of either a spun hub or cavitation. That sounds more like a lower unit or driveshaft/crankshaft that is ready for the scrap pile. But if it is grinding and chattering from a mechanical problem, you will know pretty soon. Stuff like that gets MUCH worse VERY quickly.

As far as getting the prop off, it has not been removed in many moons. The guy that "serviced" it did not have it off. You may have to destroy it to get it off. Learn from it, and in the future remove the prop occasionally and clean and lube the shaft & splines. And don't use a prop with an aluminum hub. The bronze hubs are much less apt to sieze on the shaft.

Re: 81 Johnson Help

I have tried everything I can to get that prop off to no avail.....

Dont know if the pics will help but here goes....

It almost feels as if the prop is fused onto the threaded shaft that its mounted on,and the shaft spins with the prop

I banged,pryed,and tried a gear puller?

Also Fr I may have actually mistated the mid range VS top range meaning at low rpm it does ok but when I take it up to plane Ill be going along then the problem ocurs after backing it down to mid range it goes back to normal then when I take it back up it happens again.(almost like the motor has to catch up,if that makes sense)

Any suggestions for the prop,and FR does it sound more like the hub spin after the explanation?

Thanks guys!

Re: 81 Johnson Help

Actually, it is very easy to prove whether the hub is spinning or not. Put the prop nut and cotter pin back on. Then make a mark on the prop nut and another mark on the propeller itself, aligned with the first mark. Then run the motor till the suspected slippage occurs. Stop the motor and check the marks. If they are no longer aligned, it slipped. But if they are still aligned, repeat the test, there is a slim chance it stopped slipping in the same location. A repeat of aligned marks pretty much rules out hub slippage.

Explanation: The hub and nut are fixed (splined) to the shaft. Between the hub and prop itself is a rubber cushion. If it slips, the prop more or less stands still and the hub (and shaft) spin inside it.

That prop is badly corroded onto the shaft. I would be very suprised if you get it off without destroying it. That may consist of cutting or burning it off. Drastic measures, yes. The alternative is leave it on there.

Re: 81 Johnson Help

After the pix I got a comment that the prop appears to be on backwardsDoes that theory fly?If it were on backwards the boat wouldnt move would it?I think I may be a little over my pay grade and Im gonna take it to a local prop guy to see what he thinks Whats a fair price to remove a stuck on prop and replace it with a new one generally speaking?Am I going to have a problem finding a prop for this motor or are they like tires?Some parts seem to be hard to come by for "vintage" motors?

Re: 81 Johnson Help

That prop is on there right and besides being stuck there is probably nothing wrong with it.
I'm sure the problem is with the boat. Put that outboard on a conventional v-hull aluminum boat and I bet you won't have any problems.
I had similar problems with a 9.9 Merc on a 9' inflatable zodiac.
Position the motor in the lowest setting and try putting some more weight in the stern and see if that helps.
Props are available for that motor but the non thru hub exhaust props were only made for a few model years. I think from 78-81.
I would leave the prop alone since it appears to be in good shape and when the time comes to remove it cut it off with a grinder.

Re: 81 Johnson Help

Just wanted to post an update,maybe it will help others.......

Thanks to all that posted and it turns out that most were right!

I had both problems,prop hub slipping and bad set up (cavitation)

Took it to a prop shop and they cut the old one off which was a 12 pitch prop,they ordered me a 9 pitch prop which they said was better for pulling loads which a duck boat is built to do.They also put a cup on the prop blades which they said would catch and throw the water rather than spin the water off (cavitate).

This along with dropping the motor down a notch did the trick,motor/boat run great,no problem getting on plane and even with a full load of gear get appx another 2-3 mph out of it!!

Thanks again for the help and suggestions!

Re: 81 Johnson Help

FWIW I have a 1981 Johnson 25hp too. 3 blade, 9 1/4" dia x 11" pitch prop comes standard with the motor.