'78 Johnson 15hp - troubleshooting

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Nehalem, OR
Hi all! Just bought a 1978 Johnson model 15R78B 2-stroke to go with a 12ft Gregor aluminum I picked up last month— I'd really appreciate some help getting it running right so I don't wind up stranding my nieces and nephew in Nehalem Bay this summer.

I just posted a video of motor running here...today was the first time I started it.
[media]https://youtube.com/shorts/GO7WBKN16us[/media]

I've never worked on an outboard, and am pretty unfamiliar...but have worked on some 2-stroke '70s dirt bikes back in the day.
I put new plugs Champion L78V into it, replacing the L77JC4 resistor-type plugs that came in it !?

Seemed to start up fine, but unsure if water is coming out of all the right places and if it's supposed to be so...*bouncy*?
Motor dies at idle, and the idle speed knob on the side of the motor doesn't move anything when you turn it.
After reading online, I'm very scared of 'over revving' the RPMs when the motor isn't in the water...unsure how concerned I should be.

Another issue is that motor doesn't want to shift in/out of gear -
Depending on where the prop is, it will not shift into forward or reverse occasionally unless you turn the motor over slightly (with pull cord or by turning the prop by hand).
When in gear with motor off, spinning the prop by hand turns the motor over regardless of which way you turn it; unsure if this is normal?
Prop actually turns (as seen in video) even when in neutral.
I unscrewed the 'lower unit' screws a bit and oil that came out of shaft wasn't milky...seemed pretty viscous and had slight green tint...I'm assuming good gear oil.

Observations, resources, and advice appreciated!
Excited to have found the forum and to own my first craft.
 
Sounds fine. It will be a bit jerky. It will be hard to shift without prop turning unless every thing happens to line up. As far as the idle that knob on the side might need everything attached to it cleaned up so it will move smoothly. You may have to tweek the low speed knob a bit .
 
Congrats on your purchase and thanks for sharing. You may also want to post this on the Johnson Evinrude iBoats forum. Lots of good help there too.


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First, ditch the muffs and put it in a trash can. You’ll get a better idea of the condition of the water pump this way.

2nd, it sounds like it might only be running on one cylinder. You can pull one plug at a time to check for this.

I would do a impeller and carb clean/rebuild as a matter of course and work out the shifting issue while the lower unit is off. Probably just needs adjusting.
 
CHANGE the LU lube and REPLACE the impeller before doing anything else! May also need to replace fuel lines if old ones too, as they are not ethanol E10 fuel rated, due to the alcohol content.
 
RaisedByWolves said:
First, ditch the muffs and put it in a trash can. You’ll get a better idea of the condition of the water pump this way.

2nd, it sounds like it might only be running on one cylinder. You can pull one plug at a time to check for this.

I would do a impeller and carb clean/rebuild as a matter of course and work out the shifting issue while the lower unit is off. Probably just needs adjusting.
Agree on all these points.. you saved me alot of typing! Lol

Sent from my SM-A526W using Tapatalk

 
Right off the bat get rid of the L78V spark plug and either put the old set of L77JC4s in there or get a new set in there. Much better spark plug specially where idle quality is concerned.
The overboard indicator is working however is is exactly what I called it. An indicator. It says the pump is working but not how well.
Your engine is 44 years old. They are bulletproof but it will need maintenance. A complete fresh waterpump, not just an impeller. New fuel lines, possibly a carburetor cleaning. New gear lube, grease the propshaft, grease the engine and throttle linkage.
From the sound of it the sync and link has been tampered with but there is also a possibility the engine is running really rich. Try leaning the idle out which will raise the RPM at idle as well as smooth the engine out. Do not mess with the adjustment on the throttle shaft roller on the carburetor. That is there to set the pick up timing of the mag plate to the carburetor throttle blade.
Purchase nothing but OEM parts!!! They work and they fit.
The gearcase is shifted by a dog clutch set up. If a clutch dog is not lined up with a corresponding gap in a gear dog it will not shift. There is nothing wrong with your gearcase.
NEVER NEVER spin the prop over while in gear and the engine not running. Good way to lose a hand should the engine fire on one cylinder.
Never turn the engine over in reverse crankshaft rotation. This will bend the water pump vanes backward.
 

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