Question about Yamaha Motorcycles

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I have a 1972 Yamaha ls2 100 cc twin cylinder. The problem I am having is with the electrical system. When the bike idles it puts out about 8 volts. When I rev the bike to 4000 rpm, the voltage rises to over 19 volts, burning out the lights. I know the Voltage regulator can cause this but I can not find one on this bike. Where is the voltage regulator located on this bike? What else could it be? Where can I find a electrical diagram for this bike?

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  • Yamaha Master
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Posted on Dec 26, 2016


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Posted on Jan 02, 2017

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SOURCE: Charging system on 2002 yamaha v star.

I posted back in your initial post here. A few ideas to consider/try:

  • normally, there would be 3 wires coming from the stator going to the regulator;
  • AC voltage measured on any pairing of these wires would be higher than 12 depending on the RPM above 1200;
  • DC voltage output would tend to vary from 12 to 13.8/14.2 depending on the RPM;
  • the best check would be to install temporarily anammeter inline with the wire coming from the regulator going to the +terminal of the battery. With this, the presence/absence of thecharging current could be checked.

Posted on Feb 13, 2009

  • 408 Answers

SOURCE: Yamaha dt 175, voltage question. When idling, my

You need new regulator and new battery.The battery works as a filter as well.If it is in bad condition it does not filter anything and in high rpm the current is very high.

Posted on Jun 09, 2009

  • 13 Answers

SOURCE: the wires going to the voltage regulator keep burning up.

Common problem with poor quality parts, the regulator is the problem, the generator is working other wise you would not have fried the wiring, you answered your own question. someone telling porkies to get more money from unsuspecting client?
The regulator controls the voltage not the generator, the generator only supplys the voltage it cannot overcharge unless the regulator is not working properly, simple!

Posted on Jul 28, 2009

  • 1 Answer

SOURCE: Bike won't start, battery bulged

Chances are it is the rectifier/regulator which is a sealed unit that has to be replaced if faulty. A bad one can cook your battery as well as your light bulbs and wiring. To check this connect a VOM across your battery terminals while the bike is running. If normal you should see about 13.5 volts. If your voltage climbs up to the 18 to 22 volt range or higher you must replace the part before you do further damage. Also be aware of the dangers of over charging a battery as it can explode and cause personal injury. If your battery has been cooked you will have smelled sulfuric acid and the battery will become hot to the touch. If that is the case you will also have to replace the battery as well as it will no longer hold a charge. When this happens the battery will bulge and this is called plate bow. By replacing both the battery and the rectifier/regulator you should be as good as new. In very rare instances it could be the stator which could cost a lot more but chances are its just the rectifier/regulator. I've seen them for very cheap prices on Ebay.

Posted on Aug 01, 2009

  • 377 Answers

SOURCE: voltage regulator putting 20 volts into battery

remove tail panel
remove r side panel
undo connectors x2

Posted on Oct 12, 2009

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I have a 1972 yamaha ls2 100 cc twin when I rev the bike it blows out any light that is on. It appears to be the voltage regulator but I can't find one on this bike. Does the bike have a voltage...

have you tested the voltage at the battery while the bike is running? you should check twice once at idle and once at the point where your lights are popping. if your battery is getting more than 14v then its possible your stater is going out or needs to be adjusted. im not very familiar with that bike but that's where I would start looking. also test your rectifier make sure its working to spec.

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