1985 Evinrude 70 Charging questions

[greasemonkeyjmj]

I have an 1985 Evinrude 70 Horse Model # E70TLCOS, the engine has been showing a charge output of around 13.8 with a fully charged battery. yesterday it started showing a output of 15.5 volts up to 15.7 volts with a fully charged battery, I don't know if its anything to do with it, or another problem all together, but my tack will all of a sudden quit working and fall back to Zero. This usually only lasts a minute or 2 then it go back to working, But yesterday the tach started registering about 500 r.p.m less than what it has been showing for WOT.

Thanks

 

[emdsapmgr]

Your engine has a simple rectifier to charge the battery. That rectifier also sends signals to the tach. If the tach is reading erratically-likely the rectifier is on it's way out. Once the tach quits registering altogether-some time later the battery will go dead. Replace the rectifier.

 

[greasemonkeyjmj]

o.k i changed the rectifier, it didn't help. when I first started the engine, it was showing 12.6 volts, i let it run for 45 seconds, all of a sudden the voltage started to rise a a fairly quick rate, it got up to 15.5 volts and leveled off. i hooked my multi tester to the hot cable going to the battery and it verified the 15+ volt output. Any ideas ?

 

[Fed]

It sounds like normal charging for an unregulated system like yours. I've seen 18 Volts @ WOT on a smallish fully charged battery with no other load connected.

How is the tacho?
If it's still erratic try working the selector switch on the back of it to clean the contacts inside.

 

[greasemonkeyjmj]

Thanks for the reply, it is a brand new tach, I just installed the new rectifier today, so it will be a few days before I can water test it to see if the tach still drops to zero.