1975 85HP alternator question

soulbmx

Cadet
Joined
Aug 13, 2013
Messages
18
I have a 1975 85HP merc outboard.
Finally got it running after it sat for a year by prev owner.

The batter voltage when off is around 13 volts or so. But when the engine is running it's around 11-12 volts, and sometimes jumps all over.. Is this normal?
Does the alternator only charge while moving forward?
Confused.

It also runs kind of rough. It had a half tank of gas in it, but it was prob a year old. I added a 1/4 of new and added octane booster to it. Should I just drain the tank and add all new? Or just top it up and use it?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,420
Re: 1975 85HP alternator question

I would use new fuel until you get it running properly. That motor has an unregulated charging system. The yellow stator wires from under the flywheel connect to a full wave rectifier which converts it to DC. The battery acts as a load stabilizing the voltage. Likely your rectifier is bad.
 
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