Yamaha F115 Volts low and Tach High

[gregdan24]

Went on a sea trial for the 2002 Sea Pro 1900 I'm considering buying. Noticed the tach was jumping around a little bit when we first running out - didn't notice what the voltmeter was reading. Then after a stop for a few casts, we headed back in and I noticed the voltmeter was dead - pegged at the bottom. Then the tach was reading high, like 7000 rpm at WOT. The speedo seemed to be reading low from what I recall, but we were doing 42 mph on the GPS, which I thought was pretty good for the combo.

I've done some searching on this in the past and now since the ride. Most of what I've read seems to indicate this kind of problem usually happens with a bad regulator/rectifier or a bad stator. I'm not familiar with the Yamaha 4 strokes though as I've only owned 2 strokes so far.

Anyone with a Yamaha 4 stroke dealt with this one before? The owner thinks it's probably just a bad ground, but I'm a little skeptical having worked on stuff a fair amount myself (including a few Merc rectifiers) and finding that things don't usually end up that easy.

Thanks in advance, -Greg

 

[Silvertip]

Re: Yamaha F115 Volts low and Tach High

A voltmeter reading "0" has one of three reasons"

1) Bad gauge (highly unlikely)
2) Bad wiring to the gauge. Possible since the tach was also irratic.
3) Inoperative charging system. Simple to check with a hand held voltmeter. Check battery voltage at the battery with engine off. Should be in the neighborhood of 12.6 volts. Note the reading and then repeat the test with engine running at 2000 rpm. Voltage should be in the 13.5 -14.2 volt range give or take a tenth or two on each end of the spectrum.

 

[gregdan24]

Re: Yamaha F115 Volts low and Tach High

Thanks for the info Silvertip. Just heard from the owner said he found a bad connection on the fuse in the wire to the console. Wiggled that and the tach straightened out but the volt meter is still dead. So your number 2 seems to have hit it.

According to his meter the battery was holding 13 volts and the output from the motor was 15 volts. Sounds like that reading was at 1100 rpm on muffs. Not sure how he checked it or where he measured at the motor, but not sure why it would read that much different at the battery vs. at the motor.

I know my Mercs with rectifiers always read high, but 15 volts sounds high for a motor with a regulator.