50hp Johnson reving up high on its own

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wilson973

Cadet
Joined
May 22, 2010
Messages
24
Just got done cleaning the carbs on my friends 2000 Johnson 50hp motor. after starting it up it would idle fair, if i gave it some gas it would level out. When reving the engine up, about half the time it would rev up really high and I could not cut it off. The only way to cut it off was to pull the gas line off. The key would not cut it off. Now if it is idling normal I can turn it off with the key. 1st off what makes it idle to wide open on its own, (the butterflies on the carbs are even closed) and 2nd why cant I turn it off with the key when this happens. Any help will be greatly appreciated. Was hoping to hit the river tomorrow.
 
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Daviet

Fleet Admiral
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Sep 24, 2008
Messages
8,958
Re: 50hp Johnson reving up high on its own

Were you running it on a hose and reving it up, if so you are luckey it didn't explode. You SHOULDN'T run an engine above a high idle (1500 rpm) with no load on it. You had a run away and are luckey it is still in one piece. Put it in the water and in gear if you want to test it at high RPM.
 
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wilson973

Cadet
Joined
May 22, 2010
Messages
24
Re: 50hp Johnson reving up high on its own

I was not trying to rev it up. It just done it on its own.
 
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cdn-pk

Petty Officer 2nd Class
Joined
May 20, 2009
Messages
162
Re: 50hp Johnson reving up high on its own

Well air leaks in the fuel lines/ cylinder will cause surging of the rpm. but sound like something else is not right. turning the ignition off should ground the spark.
 
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Daviet

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Sep 24, 2008
Messages
8,958
Re: 50hp Johnson reving up high on its own

You said in the first post "When reving the engine up, about half of the time it would rev up really high and I could not turn it off with the key" I was taking that statement to mean that you were running it faster than a high idle.
 
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