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Voltage Jumping Around

bwing

Brian
I'm (still) restoring a 1983 R100RS. I think the guy before me stored it outside in the snow but that's another set of issues.

The current problem is a voltmeter that hits the maximum voltage peg when I'm at a constant speed (around 4,000 RPM). It spikes up and sometimes gets caught up there. Physically tapping on it brings it down to the more normal 12.8V. Then it'll spike again. I'd say that it spikes about 30% of the time. I'm running an Odyssey battery that's essentially new (~300 miles on it). Interestingly, everything's fine in the mornings when I go to work. It only happens on the way home after its been under its cover (heat issue?).

I suspect the voltage regulator or it could be worn out brushes (it's got about 52,000 miles on it). Last night I cleaned the connections to the voltmeter. Am I hurting anything if I keep running it this way? All the time the bike doesn't skip a beat and seems to run fine. Has anyone else had this sort of problem? This thing's getting to be the money pit and I'm (frankly) tired of putting more money into it - just want to ride. I'm hoping for a single point fix.
 
My first suggestion was that you should check the grounds. When you say you clean the connections...is that at both ends of the voltmeter, ie, at the back of the meter and where it plugs into the wiring?

I wouldn't put much stock in a fairing mounted voltmeter. Get a simple voltmeter, even a $5 from Harbor Freight, and use it to actually see what's happening at the battery. Use some painter's tape and tape it to your tank while you ride around. Do it safely where you can look at it and not get yourself flattened by a bigger vehicle!!

I'm still leaning to a burnt out, abuse fairing voltmeter.
 
I wouldn't think it was worn our brushes at 52,000 miles, I had about 350,000 on my RS before having to change mine.

I suspect the voltmeter!
 
Those volt meters are notoriously inaccurate and sometimes downright wonky. The first thing I would do is verify the voltage behavior with a decent voltmeter. About $12 at most auto parts stores will get a cheap analog one. $20 will get you a decent digital one.

Then, if you find voltage jumping and diving erratically you should look at the electrical system. But I suspect the problem is the bike's useless volt meter.

I mostly consider them a period cosmetic accessory.
 
Use some painter's tape and tape it to your tank while you ride around.

I put mine under the map "window" on my old tank bag; it worked like a charm. Then, I went into the house for an hour or so and totally fried the LCD display ... it appears they don't tolerate extreme heat :-/

My $0.02USD
 
In my opinion, if you are getting a change in the meter reading by physically tapping on it, the first place to look for the problem is in the meter.
 
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