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Yamaha RD Charging Problems

This covers the following bikes

Yamaha R5, DS7

Yamaha RD250, 350, 400 All

We are always asked why my RD is not charging. Often the simple solution is throw parts at it. This is always not the solution. First you need to find out the problem, listed below is some checks you can so to figure it out.

What you will need is a Meter that reads Ohms, AC voltage and DC Voltage.

  1. You must have a good battery with clean and tight terminals, if you can grab them with your fingers and move the terminal it is too loose. This is why there is the 10mm bolt head as the screw driver will not provide you with the leverage to tighten it up properly.
  2. Original Voltage regulator, check voltage with the bike running. Above 2000 RPM the voltage should read 13.5 to 14.5 VDC. If it is too low or too high you can remove the cover, clean and adjust the small points set inside. (If this does not work replace with a new unit)
  3. Check your Rotor. This is mounted on the crank shaft on the left side behind the stator. Clean the 2 copper bands that the brushes ride on. Without the brushes contacting check the resistance from one band to the other. Should be 4 ohms + or – 1 ohm also check from each band to the metal outside casing. There should not be any contact or it should be open. If you do read resistance the rotor is bad.
  4. Check the plug. This is the 3 wire plug going to the rectifier with the white wires. Make sure it is not melted and the pins and wires are in good shape. Unplug and check the resistance between all 3 white wires. Should be close to all the same. Check from the whit wires to ground. There should not be any contact or it should be open. If you do read resistance the Stator is bad. Also check the output of the stator. With the bike running check the AC voltage output of each white wire. You should have 30 to 40 VACS above 2000 RPM.
  5. Check the brushes. Make sure they are in good shape and not work pass the line in the brush.