Motorcycle Repair/Yamaha xs750

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Question
I have a 1979 Yamaha xs 750 bobber that when it runs it runs great but I have ran into a problem with it. I bought a new battery and it started and ran fine. Started about ten times then when I shut it off it just clicks but the headlights real bright. I have checked all connections and they are good. When I jump it it fires right up but then if I shut it off it won't start again with out jumping it. What could be the problem

Answer

Hi Scott,

Your battery should be reading about 12.6 volts fully charged.
When you hit the starter button the battery should not go below
about 10 volts.

If the battery is charged and the starter relay is not connecting then
it might be either the starter relay or wiring.

Check for voltage on the red/white relay wire when you
hit the starter button.

If you have voltage there then try grounding the blue/white
relay wire to see if the relay clicks or not.

If it clicks when you push the button or ground the blue/white
then see if the battery voltage is getting across the large
terminals on the relay that goes to the battery and to the starter.

If there is power on the battery cable but not
on the starter cable then the relay is not connecting the two
when the blue/white is grounded which it should be.

Normally that blue/white is grounded by the starter button but
you can bypass it to see if the relay is working.

So make sure you have power to the relay red/white before
checking the other connections. There may be a fuse for that.

If the relay is passing power to the starter and it is not
turning then the starter may need work.

Let me know as all this may sound confusing at first.

Also let me know if the wire colors are correct as I may be looking
at the wrong diagrams.

Luck!

WS
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Motorcycle Repair

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Wayne S.

Expertise

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

Experience

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

Publications
Canadian Motorcycling magazine article

Education/Credentials
Licensed Motorcycle Mechanic

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