Motorcycle Repair: Honda CB900C Charging system, honda cb900c, regulator rectifier

Question
Wayne
I have an 81 CB900C.  The battery will not stay charged.  
This is the second new battery I have tried.  A fresh charge will run the bike for a while.  I checked the alternator output with instructions in my Clymers manual.  At idle the output showed positive 7-8 amps.  As I reved it up it went to down to zero, and showed a negative 7 to 8 amps at 5000 rpm.  I'm mystified by the neg reading.  When running I remove the batt cable it dies.  Shouldn't the alternator be powering the system by then?  Sorry for such a long question.

Thanks Roger Myers

Answer
Roger,
check the voltage at the battery when running
fast, should be around 14 volts. The amperage
you were reading was probably just battery
amps. You should have about 12 amps or so
output. Check the little brushes on the stator
under the right engine cover I believe.
OR separate the connector to the stator
and hook onto any two stator wires with multimeter
set on "AC" volts. Should have about 50-60 volts
there. The stator wires are usually all one color,
like white or yellow.
If the voltage is none or low there, the stator
or the little brushes are gone.
If it checks out good, check your battery connections,
fuse connectors and ground wires. Finally,
replace the regulator/rectifier under the side cover.