1978 Johnson 15hp possible miss?

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Succotash

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Hello all! New member and first post. I just purchased a 1986 Grumman 14ft flat bottom with a 78 Johnson 15hp. It came with a 40lb thrust trolling motor, battery, 3 seats, and trailer for $400. I couldn't pass it up. Anyways, I got it home and went through the carburetor, which was full of rust. The jets were totally clogged with junk. I put in some new plugs, and managed to get it running. She'll usually start on the first pull, and seems to pump water relatively well. The only thing that concerns me is that it seems to have a rough idle, maybe even a miss. Now this could be due to the fact that I start it using hose muffs (Not having water to deaden the exhaust sound). This is also my first outboard engine, so I lack a significant amount of experience with these. I'll post a video at idle speed to get a few opinions. Does it sound like a rough idle? Does it sound normal for an engine running on muffs? Thanks for any guidance / opinions!





 
Yep, got it all for $400. However, I did have to put new tires and bearings on the trailer. Still got a good deal i'd say
 
Sounds a little on the rich side.
Since this is your first OB am hoping you mixed your fresh gasoline at a minimum of 50:1 mixture to run it on?
The advice I am giving you will be the same. You will need to do this one more time after putting the boat in the water because your effective mixture will change with the backpressure provided by the water.
Start your engine and let warm. Turn your mixture screw inward or clockwise in 1/8 turn increments and let the new mixture stabilize for around 20-30 seconds. Keep doing this and the engine should pick up in RPM, smooth out, then slow and possibly spit lean.
Bring your mixture screw back or counter clockwise to the highest idle then another 1/4 turn.
The engine will never sound super smooth.......it's a two stroke!
Do this one more time in the water at the dock and you are set! Have fun and nice score!
 
Pappy said:
Sounds a little on the rich side.
Since this is your first OB am hoping you mixed your fresh gasoline at a minimum of 50:1 mixture to run it on?
The advice I am giving you will be the same. You will need to do this one more time after putting the boat in the water because your effective mixture will change with the backpressure provided by the water.
Start your engine and let warm. Turn your mixture screw inward or clockwise in 1/8 turn increments and let the new mixture stabilize for around 20-30 seconds. Keep doing this and the engine should pick up in RPM, smooth out, then slow and possibly spit lean.
Bring your mixture screw back or counter clockwise to the highest idle then another 1/4 turn.
The engine will never sound super smooth.......it's a two stroke!
Do this one more time in the water at the dock and you are set! Have fun and nice score!

Thanks for the advice Pappy. Yep, I have my ratio at 50:1. i will run it this evening and fine tune the mixture screw. We'll see how she turns out!

JMichael said:
Yea, $400 for that setup was great price even with the work on the engine/trailer and parts you replaced.
I couldn't pass it up, I have yet to see a decent deal anywhere near my home. Everyone is asking a small fortune for just a simple 14ft jon.
 
Well I took it out on the water today to test it out. Here's what happened:

Started up, but not on the first pull like it does on the muffs.
Adjusted the mixture needle as best as I could, pretty much turning it all the way to the right (lean) and It still seemed to idle OKAY.
After a little warm up time I opened it up to get some speed, and she started surging.
I gave it a bit more throttle and she seemed to smooth out some. At this point I was moving pretty good, I was almost at full throttle and it actually sounded normal.
As I reduced throttle to slow down, I heard a backfire and saw a puff of white smoke as she quit.
It took me several (and I mean several) pulls to get her fired up again, and the some condition repeated itself.

Sounds like an extremely rich condition to me. Any thoughts?
 
Even if you took it to mechanic for a tune up, your still coming out ahead.
 
I'd look into cleaning and possibly rebuilding the carb. I've got the '78 15hp evinrude. Sometimes she idles great sometimes not. I plan on rebuilding the carb, just haven't had the time yet.


https://www.leeroysramblings.com/Outboard%20Motor%20Related/OMC%20outboard%20related%20articles.html
check out this web site, good info.
 

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