1991 Mercury 40 horse outdrive running rough

Tonster

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Aug 8, 2010
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I have a 40 horse Merc that is firing on all 4 cylinders at idle, and then under power is firing on just 3 cylinders. All of the cylinders are getting spark, but the #4 is not firing. All the cylinders have good compression.
The motor has a new stator, control box, plugs, and rebuilt carbs. What could the problem be?
 
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