johnson 10R78M throttle response is crazy!

johnnyrude78

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Joined
Sep 22, 2011
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11
Took the boat out on the lake today and reached wide open throttle, heading across the lake, i turned the throttle to slow down and the engine stayed at full speed no matter where the handle was positioned. This really aggravates me when this happens. Does anybody have a clue as to whats wrong. This motor has been very slow to respond with the position of the throttle. This problem still exists even after a carb rebuild!
 

johnnyrude78

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Sep 22, 2011
Messages
11
Re: johnson 10R78M throttle response is crazy!

does this sound like a fuel delivery problem or a problem with the cdi system?
 

Silvertip

Supreme Mariner
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Sep 22, 2003
Messages
28,758
Re: johnson 10R78M throttle response is crazy!

It sounds like a throttle linkage issue. Pull the cover and see how things are moving. As you operate the throttle the butterfly in the carb should move smoothly and linearly and the timing advance linkage should advance and retard the timing.
 

johnnyrude78

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Sep 22, 2011
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Re: johnson 10R78M throttle response is crazy!

I forgot to tell you the motor doesn't do this at all when its on the stand with muffs! it responds very quick with no hesitation, but for some reason it only wants to act up in the water.
 

nwcove

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May 16, 2011
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6,293
Re: johnson 10R78M throttle response is crazy!

do you run it a wot on muffs???? yikes?
 

tomhath

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Dec 5, 2007
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814
Re: johnson 10R78M throttle response is crazy!

I forgot to tell you the motor doesn't do this at all when its on the stand with muffs! it responds very quick with no hesitation, but for some reason it only wants to act up in the water.

Yup, that's how they usually misbehave. It sounds like sticky linkage somewhere. Get some WD40 and spray everything that moves.
 

johnnyrude78

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Sep 22, 2011
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Re: johnson 10R78M throttle response is crazy!

absolutely not, just idle and a few little revs at most!
 

boobie

Supreme Mariner
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Nov 5, 2009
Messages
20,826
Re: johnson 10R78M throttle response is crazy!

You've got a prob in your throttle/spark timing linkage and you'll just have to look closer.
 

johnnyrude78

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Joined
Sep 22, 2011
Messages
11
Re: johnson 10R78M throttle response is crazy!

I found out it was excessive wear on the vertical shaft, next to the engine, it has a couple of gears that all rotate when the throttle is moved! I can rotate the tiller about an inch before the engine responds. Does anybody have any ideas for this problem?
 
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