Why does my 1986 90 hp outboard show a high voltage ie 18 when under full power and 14 when at idle?

Question

Outboard motors

I am not to sure if it has always been charging high. Excuse my ignorance but what does the alternator look like on the engine? Are they easy to replace?

Answer 1

Outboards not have an Alternator. Under the Flywheel on top is what is called a Stator, it have little coils that produce electricity as the magnets in the flywheel spin around. I not sure of what the min/max voltage is, but, the faster the engine turn the more voltage it produce. Depending on the Brand it may have a "voltage regulator" or most likely a "Rectifier" that need replaced. Normally a Stator will work or not work.
But, a shop can check this, which we know may cost $100 (Tops surely) to check. I would not if they honest $30-50 but that a hard call to make.

On a Johnson/Evinrude The Rectifier/Regulator assembly is on the left (facing front of engine) behind the throttle linkage and in front of the Spark Plug Coils. The links are examples and may not be exact to what you will see.

Rectifier;
http://www.maxrules.com/graphics/side_images/rectifier.jpg

Regulator;
http://www.outboardignition.com/Images/regulator.png

Answer 2

Sounds like your alternator is going bad. Did it originally charge at 18V? Replace the brushes and see if it will stay at 18V. If it originally charged at 12V then the voltage regulator is bad.

Answer 3

check the charge with a voltmeter at the battery. if the numbers are the same, you have two choices. you can hook another battery(that makes 2) in parallel and that will do it. the other is troubleshoot the stator and the rectifier.