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Hello All!
I'm new to this forum and to motorcycles -
I just bought a 1980 Honda CB750 F Super Sport. I'm thinking that the alternator is dead. Was running fine for a couple of days until I found a dead battery one morning. I jumped it, and it ran fine for the day. Next day- dead battery.
Thinking the battery was bad, I replaced with a new one. Worked for two days. This morning I was idling in traffic and the engine died. Tried to restart, but could only get a "click" form the the starter. I went home, grabbed the old battery that I had charged back up, swapped back in, and the bike fired right up. I rode it to dinner only to find it dead again when I was leaving. Jumped it and started to ride home- less than a mile down the road the lights dimmed, went completely black and then the engine shut off.
All I can think of is the Alternator is dead and won't charge the battery. I found a new alternator / stator package for ~$200 on eBay. Is this complicated to install for someone with mid-level mechanical knowledge?
Your help is VERY much appreciated!!!
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Administrator
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Welcome to the forum. The charging systems on the DOHC bikes do suck!  You can download the service manual from the manual thread here on the forum. It will shoe, you how to test the components. You might not need the whole thing. Also be sure to have any parts tested before buying.
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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Tools is right: check all of the components of the charging system. It could be the voltage/regulator assembly, or something within the alternator. Figure out/test before you start throwing parts at it -- your wallet will thank you.
 I would also recommend you install a Volt Meter, of some sort, after you get it sorted out. Draining the battery dead, will shorten its already-too-short life! I had two batteries, on two different bikes, leave me stranded, when they failed, without much warning. With a Volt Meter onboard, you can watch to see if the charging system is working properly, with a mere glance at the gauge. There are several types, including those made specifically for bikes, as well as automotive gauges. When your bike is idling below roughly 1,700-2,000 RPM, the system will not charge; above ~2,000 RPM, it should read 12.6 Volts, or higher, indicating that it is charging the battery (above 15 Volts, and your Regulator is not working, but it is boiling off your electrolyte...).
Let us know when you get the charging issue sorted out, and we can then assist you in hooking up a Volt Meter of your choice (they all work roughly the same, and there are only a couple of things to consider in connecting them properly, and safely). Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII
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Thanks for the reply. I will take off the alternator and stator this week and get them tested. Anything else in the charging system I should take in for testing?
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I've found a new stator and alternator package on eBay for $210. Would it be worth just purchasing these relatively inexpensive parts and installing them myself. Are there any other components in the charging system I should be on the look out for?
Your help and time is much appreciated!!!
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Check the Factory Service Manual (FSM). There are brushes, which wear out, in the alternator. The Rectifier/Regulator is somewhat difficult to test out of circuit. Essentially, check the resistance of the windings on the alternator parts, as per the FSM. Once you have AC coming out of the Alternator (yellow wires), then check to see what, if anything, is coming out of the Regulator, as per the FSM. Always have the battery in the circuit! Never run the bike without a battery installed!!!Stators, and rotors can be had, or rebuilt -- they are not rare items. I would suggest holding onto your money, until you know what you need -- then buy the necessary parts, and get it running. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII
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I have the same problem, rotor and stator tested okay, regulator tested bad, put in a brand new regulator and battery, same problem someone told me that the stator sometimes checks good when bike is not running, but still wont work when going, how would you test this?
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to test it put a volt meter across the batt terminals and it should read about 14.5 at 5k rpms and about 13 at 2500. to check the rotor put a volt meter on the ohm settings and touch inbetween the slip rings and it should be between 4-6ohms. anything more or less and its bad. check and make sure the brushes arnt near their scribe marks. you can then test the regulator rectifier. if you want to do that then let me know lol. i have an entire diagnostic flow chart with directions and everything on how to diagnose the charging system
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I did all the tests in the manual. everything tests okay, turned off I have 13.2 volts idling 12.5 volts at 4000 rpm 12.8 volts. doesnt seem right..
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the regulator is brand new, the brushes are about 1/2" before the scribe line and all ohm tests are within specs, connections all seem to be okay...
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just started it back up. NOW I have 13.5 at 4000 rpm
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well it idled for 10 minutes, then stalled, wont turn over, headlight is very dim but battery is showing 12 volts?????
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13.5 at 4k ain't enough podna. If you can ride all day and it's still over 12.5 ish volts when you quit for the day then it is ok any lower and something is messed up.
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that's the problem, I cant ride more than a couple of miles
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On Saturday, October 19, 2013 8:59 AM, icerigger [via Honda CB750'S] <[hidden email]> wrote:
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THANK YOU!!
On Saturday, October 19, 2013 8:59 AM, icerigger [via Honda CB750'S] <[hidden email]> wrote:
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Locked
