possible electrical issue?

GREENI3 · World Chat Champion Joined: 26 Nov 2010 Karma :

On the way home today I noticed the rev counter was moving up and down even though the engines rpm wasn't (ie. riding at a constant 5k, but needle suddenly drops to 4k and moves back again).
Engine noise didn't change at all.
It did this pretty much the whole journey.

And the indicators decided to flash really fast once or twice before reverting back to normal.

Am really confused as to what might be causing this.

Any ideas?

dolly3900 · Traffic Copper Joined: 12 Jul 2011 Karma :

Possible one of seveal issues.

1) Rectifier on the way out (feeding AC into the DC circuit)
2) Battery on way out (Helps with the smoothing of the output from alternator)
3) Earth issue

Hope that helps a bit
Mike

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Agreed, the speedo on my VFR used to randomly dip when the reg/rec was on its way out. Time to get a voltmeter on the battery and check it's charging properly.
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Blau Zedong · Banned Joined: 26 Jun 2006 Karma :

Islander · World Chat Champion Joined: 05 Aug 2012 Karma :

Sounds like it might be a dodgy earth connection as it's affecting more than one system.

It wouldn't hurt to meter the battery and check charging conditions as well.

GREENI3 · World Chat Champion Joined: 26 Nov 2010 Karma :

Well I checked the battery last night and was at 12.3v. Started and ran it for a while; voltages were all over the place, mostly going down!
Wouldn't go over 13v at 5k.
Swapped the reg/rec for the original that I had replaced as a preventative measure and it was sort of doing the same thing.

Had it switched off for a while then went to start again and a load of sparks came off the starter motor. It would then only click.
Checked fuses, all ok.
Then thought the earth on the starter motor might be the culprit due to looking quite dirty and the recent rain we've had.
Cleaned it up with a wire brush to get it nice and shiny and put a bit of lithium grease on it. Started first time.
The battery was then reading just under 12.5v, so stuck it on charge overnight.

Put a multi-meter across the battery at work today and was reading 12.9v, so it appears the reg/rec was at fault and possibly the earth was a contributing factor as you guys thought.
The reg/rec I bought was only £25 off ebay, so probably made in china. Not surprising it failed.