Tachometer Failure & Charging Voltage

[CDMOOSE]

My boat has twin 1999 Honda BF40s. Earlier this spring, the port engine tachometer failed, or nearly so, jumping around a bit upon start-up, but then showing no indication of rpm. Thinking the tach was faulty, and not knowing what else to do, I replaced the gauge but there was no change. Then recently, while at cruising speed, I noticed that the port engine was charging at only about 13 volts while the starboard engine was more properly at 14.8. And then yesterday, for whatever reason, the port engine was also putting out 14.8 volts and the tachometer was working fine!

I don?t know how these two circumstances are connected, but they appear to be. And I can even vaguely understand how something in the port engine charging circuitry may have failed such that it was putting out only 13 volts. But what would explain a spontaneous recovery?

All was fine as of yesterday, but I need to understand what is going on for when and if it happens again. Thank you for any insight you might be able to provide.

Al

 

[weareallnuts]

Re: Tachometer Failure & Charging Voltage

I found this info in another thread, CDMoose, maybe it will help. I have the same issue on my Tohatsu -- new tach worked well for a year or so, then sporatically, then not at all. I was just planning on replacing it until I read this info, now I think I'll check out the plugs --

Re: Tohatsu M70C warning buzzer

Make sure you have the correct spak plugs. These motor require resistor plugs otherwse the radio frequency interference from the ignition system can cause spurious alarms and or activation of the speedlimiter. I had this problem when the motor ran at approximately 4500 rpm for more than one minute. After replacing the water pump, thermostat, rebuild kits in carbs, new fuel filters, replaced temp sensor, removing head to check for blockage the problem persisted then I found the plug problem. This seems strange but it is true and it is not all that unusual. If you search the net you will find technical articles on this issue, bad thing is the authorized Tohatsu service center I used was not aware of the issue. Good Luck

And here is the link:

members.iinet.net.au/~pauldawson/iame26-spark-plugs.PDF

It came from this thread:
http://forums.iboats.com/showthread.php?t=484540&p=3371403#post3371403

Peter in SC

 

[jayyyy]

Re: Tachometer Failure & Charging Voltage

Erattic tach. and flucuating charging sounds alot like a failing rectifier or posssibly a stator.

 

[CDMOOSE]

Re: Tachometer Failure & Charging Voltage

Thank you, both, for responding. This will give me a couple of other items to consider.
Al