1999 15hp Johnson Stuttering at low RPM

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bonnetbum

Cadet
Joined
Jul 31, 2006
Messages
7
Hi guys

I have a 1999 15hp Johnson 2stk and it appears to stutter at low speed almost like its not firing right. Move past the low speed and it goes away. I have changed the plugs, no difference (They looked ok when i removed the old ones also...)
I haven’t done a compression test because I don’t have the equipment to.. Because I know that a question someone will ask :)

Is there anything I should be looking for? I am planning on putting a carb kit in to see if that makes any difference. Other than the stuttering at low speed she runs beautifully.

Any help will be much appreciated
 
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bonnetbum

Cadet
Joined
Jul 31, 2006
Messages
7
Re: 1999 15hp Johnson Stuttering at low RPM

Oh and I forgot to mention that it only happens when the motor is in water under load. Doesnt do it when im flushing her out on the shore.

Cheers
 
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bonnetbum

Cadet
Joined
Jul 31, 2006
Messages
7
bonnetbum said:
Re: 1999 15hp Johnson Stuttering at low RPM

Oh and I forgot to mention that it only happens when the motor is in water under load. Doesnt do it when im flushing her out on the shore.

Cheers
Click to expand...
Bump, I still own this boat and am having this same issue. Feels like maybe its an out of balance prop? Idle no load is fine. Anyones suggestions would be much appreciated :)
 
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racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,298
Compression test first.---A must do.-----Hope you have installed a new impeller as a precaution !
 
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daleyeah

Cadet
Joined
Jul 13, 2021
Messages
23
Save yourself the trouble and don't get a tester from Harbor Freight. I had look with one from Auotzone.
 
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bonnetbum

Cadet
Joined
Jul 31, 2006
Messages
7
racerone said:
Compression test first.---A must do.-----Hope you have installed a new impeller as a precaution !
Click to expand...
Sure did, the water stream is nice and strong.
What kind of compression numbers should I be expecting? OR how much variance is to much?
 
B

bonnetbum

Cadet
Joined
Jul 31, 2006
Messages
7
bonnetbum said:
Sure did, the water stream is nice and strong.
What kind of compression numbers should I be expecting? OR how much variance is to much?
Click to expand...
Update, got a new prop and she's running great! Must have been a slightly bent hub.

Running beautiful now. Big shout-out to ozpropellers.com.au for their great customer service and support :)
 
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