Evinrude '85 - 40hp - runs rough

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bigjohn767

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Apr 30, 2012
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My brother-in-law has an '85 Evinrude 40hp that runs rough and sometimes won't idle. He has rebuilt the fuel pump and both carbs, replaced all gas lines, and put in new plugs. It idles OK now but sometimes just shuts down. It also has what I call a "miss" in the engine. Being a car guy, I asked about float adjustments and such and he said he didn't know to check the floats. Could the floats be causing the problem? He did clean all the carb parts but I don't think he ran a wire through the jets as suggested in another post. Another clue is the lower plug appears to be wet while the upper plug is dry.

I thank you in advance for any suggestions!

John
 
oldcatamount

oldcatamount

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Re: Evinrude '85 - 40hp - runs rough

The float should be parralel with the carb body when held upside down. I doubt it's a carb issue since you have one wet plug and one wet one. Chances are that it's an ignition problem. Are the plugs the correct number and are they gapped right? A compression test might help here. A weak cylinder will also cause the symptoms you are describing.
 
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bigjohn767

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Re: Evinrude '85 - 40hp - runs rough

He has put in new plugs (I assume they are the right ones) but I didn't see him check the gap. The compression is 90 on both cylinders. Could it be a coil problem?
 
oldcatamount

oldcatamount

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Re: Evinrude '85 - 40hp - runs rough

You could try swapping the coils around to see if the upper plug remains dry. If it doesn't, the coil is the problem.
 
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