Testing for Charging Issues

[BlueR32]

My RD250 motor is still not running right and I suspect charging issues. I found this information on Oregon Motorcycle Parts: https://oregonmotorcycleparts.com/FAQ.html

I followed these steps but as soon as I disconnected the regulator/rectifier (Ricks aftermarket), the motor shut down.

What am I doing wrong here?

Finding out if the charging problem on a R5, DS7, RD250 and RD350 is the alternator or the regulator and rectifier.


To do this, start by running the bike until it is warmed up enough to idle properly.  Unplug or remove the regulator and rectifier.

Make up a jumper wire with a 2 amp fuse and run power from the positive side of the battery directly to the green wire from the alternator.

With the engine running test the voltage AC output at the 3 white wires from the alternator with
the engine running at around 4500 RPM. 

If you get 40 or more volts AC the stator, rotor and brushes are OK.  If the voltage
is low or the fuse blows, the problem is under the alternator cover.

[m in sc]

run a 12v jumper from the battery to the coils. this will allow the bike to run sans regulator/rectifier. then do the test. however, 12v to the green wire on an rd is a lot. they dont see 12v normally and you may fry the rotor.

here's my suggestion:

stator:
check continuity of each white wire to itself, should be almost no resistance.
check continuity each white wire to ground, should be zero continuity

rotor:
take brush holder off. check continuity of slip rings, should be 4 ish ohms between slip rings.

brushes:
make sure the black one is grounded
with all wiring connected, check voltage on green wire with key on. i think it sees like 7 volts max? this is what excites the rotor. it turns off after reaching 13 ish volts.

if all that is ok, then its in your wiring or the rr unit.

good luck

 

[1976RD400C]

I have checked that the rotor voltage is 10 volts, lights off, kill switch off, key on.

[m in sc]

I have checked that the rotor voltage is 10 volts, lights off, kill switch off, key on.

on a 400 or 350? they work differently.

[1976RD400C]

I have checked that the rotor voltage is 10 volts, lights off, kill switch off, key on.

on a 400 or 350? they work differently.

That was on a 400

[BlueR32]

Thanks m in sc! I will try the suggested tests and report back. I should have mentioned that I already have the relay mod in place so I should be getting 12v direct to the coils.

[m in sc]

i get it. but skip the relay and jump it direct for testing

[axldk6]

on my 74 350 , when i got it it had a no charge condition. did all the meter checks and everything passed. put on a Ricks reg/rec and had it charging again. then about 3 weeks later a no charge again! got out the meter installed new brushes i had stuffed away and still no charge. pulled the trigger on a Vape and golden . takes the worry out of several issuies with the factory dynomo system. "No one will ever know" God bless America and never forget !

[m in sc]

while i agree, thats a big nut to drop money on. fwiw, ANY rr for a sohc cb750 will work. juat has different wiring colors.

honda:
black is switched power (brown on yamaha)

green is earth(black on yamaha)

white is armature (to green wire for brush on yamaha).


red same on both, battery directly.
3 white/3 yellow are ac leads.