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Motorcycle Repair/1997 yamaha virago 750 charging system

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Question
My battery drains after a couple days on short rides to work.At idle i get close to 14 volts when i increase rpm the voltage drops to around 12.5 also when headlight to high beam or brake or turn signal applied voltage drops even on increase of rpm any suggestions on what to check thank you ed

Answer
Hi Ed,


I am not sure if your battery is okay but you will have to have it charged, load tested or replaced
to test the bike's charging system. Tighten the cables on both ends.

You have to determine if the stator or the regulator/rectifier is at fault
or something else entirely.

The stator should have a connector coming out of the engine which has
three white wires in it.

Disconnect the plug and with a multimeter check that none of the three white
wires are grounded. They should not have any connection to ground or the bike
frame.

If they pass that test then you can start the bike with the plug disconnected.
Set your multimeter on "AC" voltage.
Check the voltage between any two of the three white wires.
Speed the engine up a bit and watch your voltage readings.
Between any two of the wires should put out about 30-60 "AC" volts.

If this seems okay then it is logical to check your regulator connector, ground
and wiring. Finally reconnect the connector and put your multimeter on the battery
terminals. See what the "DC" voltage is at a fast idle.

If it is reading the same as the battery or above 15 volts then shut it down
and replace the regulator.

If the stator reads low or no voltage on any two of the three wires
then the stator may be gone.

Do these tests with a known good battery to prevent any problems
arising from a shorted battery.

If you get the stator, regulator and battery fixed it should work.
If you see any place the wiring has been hot that might be a problem too.
Check and clean any connectors relevant to the charging system.
A bad connector will also cause a loss of charging current.

You might have one bad stator winding that is resulting in a loss of total power
when the engine speeds up. Check the stator as described above
and make sure any two of the three white wires have substantial AC voltage.

Let me know if you need more info.

WS

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Wayne S.

Expertise

Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.

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Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

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Canadian Motorcycling magazine article

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