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Discussion Starter · #1 ·
Over the last few days my starter seemed to be struggling a little to start the bike. Yesterday I tried jump starting from my car, and the bike battery began to stink of sulfur while struggling to start, but the bike did start. Went out for a brief ride and shut her off, then had to running bump start to get home. Today jump starting from a running car did not work at all. I decided to try a bump start on a hill (fortunately begins at my driveway and is nice and long so I can start cold) and that worked. Once the bike starts all is well: normal charging voltage (14.1-14.4), the bike runs normally and all electricals are functioning. No smell from the battery when running, and when I shut off the bike the battery stays at 12.5, which is what it has shown for as long as I've owned the bike. I did the plug-in 30A main fuse upgrade when I got the bike.

I connected my multimeter to the battery posts. Key off, the battery is about 12.4 volts. At the "ACC" position voltage stays the same. When the key is switched to "ON" position, the voltage drops dramatically, down to 8.9-9.0. I disconnected the headlight fuse and repeated, still the voltage drops to 10.4-10.6 when switched to "ON" without the headlight connected. I tried disconnecting each of the other fuses, no effect. Once you hit the starter button the voltage drops down to 6 or 7 volts and the solenoid buzzes until the voltage drops below 6. Shut off and the battery recovers to 12.5 volts, and I've been topping it off with jumpers to a running car.

I removed the starter, put it in a vise and applied 12 volts. It spins fast and quiet. Reinstalled the starter and applied 12 volts via a jumper cable from my running car (lightweight motorcycle jumper cables with small pointy clamps). The starter tries, but will not turn the engine.

Ideas? What is causing the big power drain when I turn the key to "ON"? Why doesn't the starter turn even with direct 12 volts applied from a running car?
 

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Maybe a starter ground issue.

Try running a jumper lead from the negative battery terminal to the starter motor rear case.

If this gets no joy scrape a little paint from the starter motor centre body and try there.

If it goes with the lead to the rear body you need to clean your grounds. If it goes from the centre you likely need to clean the starter internally and do the starter ground mod.

As to the power drain. Keep disconnecting things one at a time until you stop detecting the drain.
 

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Most but not all your information suggests a weak or failing battery. In addition to previous suggestions I would disconnect the bike battery (at least the positive cable) and connect the car battery to the bike battery leads, bike battery out of the circuit. Car not running (to keep the car charging system from confusing the test) and do not disconnect the car battery until you shut off the bike again. If bike starts normally it supports replacing the bike battery. Size of car battery is irrelevant.
 

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'84 CX650E that is evolving into a GL500
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Re size of battery, I've been using U1 size batteries (commonly used in garden tractors) on my winter machines for reliable starting in the depths of winter for decades and the only modifications needed were a place to mount the bigger battery and longer cables to reach it. The main thing is that it has to b a 12V battery, which is pretty standard these days.

What is causing the big power drain when I turn the key to "ON"? Why doesn't the starter turn even with direct 12 volts applied from a running car?
That is most likely the current being drawn by the ignition system. You can test that by turning the kill switch to Off (with all of those same fuss removed) before turning the key on and observing the battery voltage.
If the voltage still decreases when you turn the key On something is drawing current that shouldn't be (any electrical accessories?)

disconnect the bike battery (at least the positive cable)
SAFETY WARNING: If you are going to disconnect one cable from the bike's battery it should always be the negative cable and if you are going to disconnect both you should always disconnect the negative first.
The reasoning behind that is that if you are undoing the positive while the negative is connected and the tool touches ground it will short out the battery, resulting in big sparks, possible damage to the battery and in many cases burns because the tool can get very hot very fast. BUT if the tool you are using to undo the negative cable touches ground that cable is already grounded so nothing will happen AND if the negative cable is disconnected first and the tool you are using to undo the positive touches ground the circuit won't be completed so nothing will happen then either.
BTW: It is advisable to remove any rings while you are working on or around the battery too. Our high school auto shop teacher told us about careless mechanics being burned because they undid the positive first and a ring that was touching the wrench brushed against ground, completing the circuit. Not much has changed in the half century since except that now you can find countless images of "electrothermal ring burns" online.
 

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Discussion Starter · #5 ·
Most but not all your information suggests a weak or failing battery. In addition to previous suggestions I would disconnect the bike battery (at least the positive cable) and connect the car battery to the bike battery leads, bike battery out of the circuit. Car not running (to keep the car charging system from confusing the test) and do not disconnect the car battery until you shut off the bike again. If bike starts normally it supports replacing the bike battery. Size of car battery is irrelevant.
Trying this now. I really don't want to do Geneva-on-the-Lake in my Ford Ranger.
 

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Discussion Starter · #6 ·
Trying this now. I really don't want to do Geneva-on-the-Lake in my Ford Ranger.
Thanks Rich! The bike starts and runs fine off a pair of full-size jumper cables between the Ranger and the battery leads with the bike battery disconnected. Dead battery. The 12.5 voltage really means nothing when you have insufficient cold-cranking power. Batteries die different deaths. This one held up pretty darn good all things considered, three years stored outside and recently did a cross-country trip in extreme heat.
 
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Discussion Starter · #7 ·
Thanks Rich! The bike starts and runs fine off a pair of full-size jumper cables between the Ranger and the battery leads with the bike battery disconnected. Dead battery. The 12.5 voltage really means nothing when you have insufficient cold-cranking power. Batteries die different deaths. This one held up pretty darn good all things considered, three years stored outside and recently did a cross-country trip in extreme heat.
Oh boy. Not done yet. I jumped the bike with the battery in place. It starts and runs, but the voltage at battery when revving above 3k or so jumps all the way to 16+ . Help?

The problem was with the stupid little accessory voltmeter/phone charger. Never believe readouts from anything but a good multimeter.

Dead battery, looking for a new one now.
 

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Check that you have battery voltage at that sense wire connection to the regulator.
 

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It shouldn't go above 15V.
The first thing I would do is verify that your meter is accurate (connecting it to a 9V battery to see if it says 9V is usually good enough).
If the meter is good I would suspect the sense wire. If the problem is just oxidization in the contacts in the regulator/rectifier connector that can sometimes be fixed by simply unplugging and re-plugging the connector to push the oxidation out from between the contacts. This should be done for all of the connectors periodically, especially the stator connector (3 yellow wires).
If that doesn't fix it the problem is probably poor connectons inside the 4 decade old wiring harness . The proper fix is to peel back the tape on the harness and refresh all of the connections inside it but the symptom can usually be dealt with by connecting the black wire from the regulator/rectifier directly to battery +.
 

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I dealt with this recently helping a friend with an '03 Yamaha something. We went embarrassingly far down the bad starter/ blocked reduction gear hole before discovering the battery had a few bad cells.
 
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Silly question, did you check the water in the battery? I had the same problem and bought a new battery, while changing it I noticed that the water was low, filled it up and have been using my old battery for my fishing boats motor.
 

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Discussion Starter · #12 ·
Silly question, did you check the water in the battery? I had the same problem and bought a new battery, while changing it I noticed that the water was low, filled it up and have been using my old battery for my fishing boats motor.
The old one was a sealed battery. I replaced it with a standard lead-acid battery as an interim measure, so I'll be staying on top of the water levels and taking the battery inside the house for the winter.
 
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