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Hey everyone, I've read through numerous forums on this page, and decided to ask my own question.
I recently acquired a '80 750K, and after jumping it, I was able to get it started, and I drove it home. At times, while driving, I noticed some hesitation every once in a while. Once I got home, I ran inside for no more than 5 minutes, came outside to start the bike, and nothing... No lights, no sound, nothing...
I hooked it up to my car (engine off), and the lights turned on, but it wouldn't turn over, I ran through all the tests on the rotor, stator, and RR, and they all passed except for the one test on the RR, telling me I have a bad connection from the battery (+) through the ignition switch to the switched +12V supply-input on the RR. Fuses are all good, so I think it's my ignition switch, which I think I also just shorted out, because I get nothing when I turn the key, even with jumper cables on. So I ordered a new switch, as they aren't expensive at all. Hoping that at least gets my lights to come back on so I can have power again.
I also noticed when I was checking on the stator that one of the brushes was VERY worn... Could that be why my battery isn't charging even though the RR, rotor, and stator all passed their tests? I ordered new brushes as well, again, since they were very inexpensive.
I got it started yesterday, and even rode a little bit, but after maybe 5 minutes, she died, and I had a very hard walk up a large hill...
Once I got it back home again, I tried to start it and nothing happened, again no noise or anything. I hooked it up to jumpers, got it started, revved it up to about 5000rpm, and let it run for a little while. But once I disconnected the cables, she died immediately...
I had the fuse cover off, and without really thinking I put the key in and switched it to the run position, and a brass key that's on my key chain touched one of the fuse connectors, and I heard a pop from the ignition switch, and now I don't get anything, which is why I ordered a new on. Might just try to repair my current one with pieces from the new one.
I'm really hoping it's just the brushes and ignition switch...
What do you guys think? Any help is appreciated!!
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Administrator
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If you have one or more dead cells in the battery, it'll run well enough with a jump, but have nothing for starting. Check the battery at your local auto parts store. It should be between 12 and 13v with no load.
My first guess is bad battery. Get that checked and resolved, and then check the other components (rotor/stator, wiring, rectifier/regulator, etc). At least it runs...that's the best part.  Before you dive too deeply into this, download the FSM from the home page of our happy little forum. There are some good troubleshooting techniques for the electrical system.
Get back to us with your observations, and we'll try and help you more.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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It's a new battery, and it reads 12.4V with the jumpers on it, but once disconnected, it starts draining... All my connections and wiring are good. I literally checked every test on the rotor/stator and rectifier/regulator, and they were all fine. Rotor checked out at the right ohms, I got the right voltage from the stator, and the right voltage from the rectifier. I don't think it's the rectifier, because when it's running, and I rev the engine, the battery doesn't go past 12.5V... And when I push the start button, the battery drops down all the way to +/- 8V, then back up to around 12.5V once it's turned over... Could that be because of the worn brush?
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Administrator
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OK, on the battery. It is new, but only reads 12.4 WITH the jumpers on? If you have absolutely nothing connected to the battery, what does it read? A battery at rest with nothing hooked up, should read 12.6.
Even in the bike, with it off and no accessories, should still read 12.6.
It is entirely possible that the battery is already bad. I had that happen. Read fine on voltmeter. AS soon as a load was placed on it, flatline.
Now I ALWAYS by my batteries unfilled. Battery life starts when it is first filled, not when it is installed. So, you could have gotten a "new" battery that sat on the shelf a year already. That battery is now a year old before you even used it.
The ride IS the adventure. The destination is just to get gas!
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Oh, it was a NEW battery. I had to fill it with acid. I'll try connecting it to a charger when I get home from work and I'll let it charge overnight. But with the jumpers off, I was getting a reading of +/-10V... Could that mean that my battery is already bad?
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Administrator
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Maybe, hard to say. After you filled it, did you fully charge it before putting it in the bike? Also, what amp did you charge it at. Small batteries like this prefer 1 - 2amp charge rate. Higher rates could potentially cause damage or shorter life.
The ride IS the adventure. The destination is just to get gas!
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It was not fully charged... I'm charging it with a 1 amp charger
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Administrator
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Yep, you must always charge a new battery first. A car battery isn't a big deal cause of the size, but powersports need it.
The ride IS the adventure. The destination is just to get gas!
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So, I checked the voltage of the battery this morning, and it read 12.6V. Should I check it when it's disconnected from the charger, or does it not matter?
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Administrator
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Yes, please check the battery after an overnight charge, with the leads disconnected.
It's entirely possible the battery was bad from the get-go. I'd recommend taking the battery back to where you got it, and if they have the capability to load test it, have them do it. Otherwise, you may be able to exchange it with another, if they're amenable to that.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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Sounds good. When I get home, I'll disconnect the battery from any load, and I'll take a look at the voltage.
Assuming it stays at/around 12.6V, I should be good when it comes to my battery, correct?
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Administrator
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Barring any internal problems with the cells, yes, you should be good to go.
Several things could be stressing the battery:
Starter electrical issues (worn brushes, corroded connectors, etc)
Some lights that are stuck on due to wiring or bulb sockets
Too heavy a bulb in the headlight (presuming someone put in a high wattage bulb)
Not enough voltage/current from the alternator and Reg/Rec (check the 3 yellow wires from the alternator to the Reg/Rec)
Keep in mind that the system doesn't really charge the battery until the RPM is at 2000 or higher. At about 5000 RPM, you should see between 14 and 15 vdc at your battery posts.
I hope this helps.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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Just to reiterate what Luke and Rerun said: I've ruined brand new lead-acid batteries by not following the instructions - fill and charge fully (over night at 1 or 2 amps) before use! They'll croak if you just fill it and try to charge it at high amperage or try to jump start them.
You may have acceptable voltage after charging but do a load test to be sure the battery isn't damaged. You take it any auto parts store and they'll do a load test on it for free (just be sure it's been charged for a while first).
89 VN 750A - Given to son-in-law
79 CB 750K-sold 3 May 21
78 CB 750K
77 CB 750K
77 GL 1000 x 2
77 CB 550F
Holton, KS, US
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I'll for sure do that. When I got home, I disconnected the battery from the charger, and it read 12.8V
I also opened up my starter solenoid, and noticed the thin fuse was blown (Which is why I'm not getting anything with he turn of the key). So I just ordered a 5 pack of those.
I also checked the ohms of my rotor, and it read 1.1 ohms. I originally heard that the rotor was only bad if it didn't read at all, bbut I watched a video of a guy testing different rotors, and he was saying they're only good if it reads 4.5-5 ohms... Is that true? If so, it looks like I'll be ordering a new rotor as well!
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Administrator
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I have bought several Caltric stators, and reg/rectifiers and never had a problem with any of them. Never used one of their rotors though, but would not be afraid to try one.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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I have one ordered, ad it should be arriving next Tuesday. Meanwhile, the stator brushes will be arriving on Saturday.
Not that it really matters, as I have to wait for the fuses for the solenoid to arrive, but I'm hoping once I get everything, and install everything, it will be up and running!
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Administrator
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I always replace those metal fuse strips with a wire in blade type fuse holder, and a blade type circuit breaker, both available at any automotive parts store, for around $10.00.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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I'll have to look into that for sure!
Thanks, Tools!
And thank you to everyone else for the help!
I'll let you guys know what's up once I've gotten everything in!
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Rotor is coming today (Gotta love same-state shipping!), ignition switch is also coming today, brushes are coming tomorrow, and last, but not least, the fuses are coming on Tuesday!
I'm ready to get this bad boy back on the road!!
I'll keep you guys updated!
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