79-82 Honda cb650 charging problems

– – – Scroll to bottom above the comments for an update…

Jesus Fucking Christ. My rotor shit out again yesterday.
Where do I start? This is going to be a long post.

So, the 79-82 Honda cb650 has a shitty charging system.
I realized I’ve never made a post explaining in detail. So, here it goes…

Let me back up a step… In the earlier 70’s, Honda’s had a solid magnetic rotor and the housing was filled with oil. This was good. Honda’s rarely ever had charging problems… and if they did… it was because the regulator rectifier went bad, which was easy and cheap to replace.

In 1979, Honda tried a different type of charging system for 4 years. They went with a rotor which was wound up with wires inside of it, and the housing was not filled with oil. Shit would get hot. Real fuckin hot. Long story short… the rotor would often shit out. My rotor shits out about once a year.

Pic below. Left to right.
new rotor, new regulator rectifier, new stator
These are the 3 components in the charging system.

This is the way the used parts all sit on the bike. (I already took the rotor locknut off)

Where it all plugs in under the seat.

Ok… this is where it gets tricky.

The main thing that will go wrong with the charging system is the rotor.
There are 2 different ways that the rotor will shit out:

The wire on the rotor will physically snap as seen in the pic below. Once the wire snaps, no more charging at all… nothing. It will instantly start draining the battery. You’re not going to make it home. Battery will shit out in about 10-20 mins. Maybe less.


The wires will visually appear fine, but the reading will be way above the spec 4-6, as seen below. Apparently that means there is an “open” in the circuit. Not sure what that means. Anyway… if this is the case and there’s an “open”, the charging system will still kinda work, but it will be erratic. It won’t directly start draining the battery… at least not right away. It will range from 9 > 12 > 7 > 10…. get what I mean… it will be erratic, rather than holding at the 13.5 – 14 like it should be. So… if this happens, you have a good chance of at least making it home before the cycle shits out completely.

Check out what the Haynes manual has to say about it all.

Getting the rotor off can be a pain in the ass. You need a “gear puller”. Pep boys has them. Make sure you back the lock nut out 1/4″ before trying to use the rotor puller.

Once you replace the rotor, stator and regulator rectifier, shit should be good again. 13.5 at idle and around 14 at 4K rpm.

Ok, so… you know how to replace the 3 items in the charging system.

Let me go into detail about other contributing things about why this charging system sucks balls.

I’ve come to the conclusion that heat is one of the main thing that breaks down the rotor. The stock header sits directly next to the stator cover, so I swapped out to a Mac 4-1. This eliminates extra heat on that side. I also installed an oil cooler to keep the engine a tiny bit cooler.

There are other factors that could make the rotor shit out. Not sure if i’m going to say this right, but if you have something in your wiring which is pulling extra amps, or the circuit isn’t flowing right, this could cause more strain on the charging system. So, basically, just make sure your wiring is the way it should be and your fuses are all good.

So, regarding my situation…
I’ve never had the charging system last longer than a year. I’ve done literally everything I can think of to prevent or offset the rotor shitting out:
– Every piece in charging system is brand new
– Different header/exhaust
– Oil cooler
– Rebuilt my entire wiring harness (check that out here)
– Double checked every connection numerous times

And the rotor still shits out on me. The aftermarket rotors have a thicker gauge wire to prevent it from shitting out, and over time… it still shits out.

I’ve researched this problem for the past 3 years, and there seems to be no real solution other than always keeping a backup aftermarket brand rotor and regulator rectifier on hand, so when your stuff shits out, you have a back-up ready.

One other thing to note is the stator rarely ever goes bad. Every time my rotor shits out,… it takes out the regulator rectifier with it, but the stator remains good. But… if you’re replacing all this stuff for the first time. Def make sure you replace all 3 just for a peace of mind.

Resources to buy the new parts:
Dime City Cycles – for lower watt bulb

Good luck. This is the only flaw of this cycle. Unfortunately, it’s a big flaw.

Update – March 2013

I’ve been running all the new charging components as outlined above… with a lower wattage headlight bulb from dime city cycles, and shit has been good for over a year now. No problems. Also… I have a custom switch to keep my headlight off during the day. So… try the lower wattage bulb, but keep it off when you can. It seems to help in conjunction with all the new charging components… and oil cooler, and streamlined wiring.

68 responses to “79-82 Honda cb650 charging problems”

  1. Richard says:

    You totally jinxed it. At least it will be good for another 3000 miles after you fix it. Hopefully it will work to Ohio and back.

  2. admin says:

    Dude, I know…
    I def jinxed it on sunday. Fuck. oh well…

  3. Richard says:

    Better now, then on the road.

  4. Adam says:

    I really thought our new wiring harness we made for it was going to solve this problem but I guess not. We need an electrical engineer to figure this shit out.

  5. Aaron says:

    Perhaps you can get a custom finned cover fabbed up?

  6. Todd says:

    Get a new/newer bike?

  7. admin says:

    We’ve actually talked about that before. Shit, I wish I could swap out for a magneto or something, but I’d need a kick start.

    Nah, fuck that.

  8. Maybe you could run an ammeter on that bike for the next couple months to monitor your electrical consumption. You’d be able to see peaks easily enough and this might hold the answer.

    The broken wire, if not mechanically broken by something flying around inside the case, is likely melted from too much current. I have my doubts that this compartment gets hot enough just by convection/radiation from the nearby header.

    You can pick up a cheap and reasonably small ammeter at most auto supply places.

    Too much consumption will cause failures your charging system is working overtime to meet the high demaand. Too little consumption, from perhaps a battery that won’t take a charge, will leave the system trying to shunt too much power (and resultant heat).


    p.s. – an “open” is simply the opposite of a short. The latter is two conductors touching when they shouldn’t. The former is two conductors not touching when they should be.

  9. admin says:

    Thanks for the input Jason.
    Yea, this has been stumping me for 3 years now. And every other owner of this bike has the same types of problems.
    Is it possible it’s just destined to be shitty and there’s no solution?

  10. mick says:

    i also would think that it would have to be something more major than too much heat. seems like a flaw that would have been caught in production.

    maybe try a new battery for a few months?

  11. Aaron says:

    Hm, the idea of it being due to inconsistent high-draw is an interesting one. I wonder if an inline capacitor would help smooth out the draw it sees.

  12. jonny says:

    tech madness

  13. If it were mine, I’d try two things.

    1) hook up an ammeter as mentioned and monitor current draw. This would expose intermittent shorts and other problems.

    2) Rewire the bike. Japanese bikes have a couple hundred miles of extra wire anyway. Make your local junkie very happy by handing over a huge fucking ball of extra wire so he can burn off the rubber and sell the copper for a hit.


  14. Adam says:

    I like the ammeter approach to hopefully take note of variations. It’s always been my thought (without having a great understanding of electrical systems) that the bike under specific circumstances is doing something with current causing it to fry the weak link in the rotor and not because of engine heat.

    Because of this, we simplified the wiring harness last year when Ed rebuilt the top end, but unfortunately it didn’t solve the problem.

    I’m all for the ammeter monitoring. Let’s figure this out.

  15. admin says:

    Like adam said, him and I rebuilt my entire wiring harness last summer. Cut out all the unnecessary stuff. I only have the wires needed to run and charge the cycle. And every item in my charging system is brand new. Shit ran great for a year. No charging problems at all. 13.5-14.5 all day, everyday. And then out of no where, it shit out on me again.

    I like the idea of hooking up a ammeter. Can you explain where I hook it up? Do I hook it up to the battery, or do I hook it up to the wires that come off the Stator?


  16. Ed & Adam,

    You must use a DC meter. Do NOT hook it up between the stator and the reg/rect. Hook it up IN LINE between the battery + and the main hot wire to the ignition. This will show total current used by the bike.

    Ammeter measure current flow, and thus need to be inline just like a water meter your house. Voltmeters measure potential across two conductors and are mounted across + and – terminals showing their difference.

    Cheap meters can be found at auto places but unfortunately they are 60A models and I don’t think they would have the sensitivity to show variations in the range you’re interested in. I think a 30A one would be good.

    It’s ugly, but you’re at wit’s end and will have to deal. . . here’s a cheap one for $7. Any 30A DC ammeter will work.



  17. admin says:

    Awesome Jason.
    Good input. I’m definitely going to try this and see what we find.
    I may have some questions later on once I hook it up.

  18. Also. . . have you seen this? A very good logic/testing flowchart: http://www.electrosport.com/media/pdf/fault-finding-diagram.pdf

    Are you running halogen lights or any devices that would make your bike draw more current than stock? These charging systems were designed to just cover the requirements of the bike (and some would consider that they missed the mark ;-0 )


  19. admin says:

    Cool, yea, I’ve seen that flowchart.
    I am not running halogen lights.
    Nothing should be drawing more current.
    I eliminated a lot from my wiring.

    The only things I have in my wiring are:
    – headlight (high-low)
    – taillight
    – electric start / kill switch
    – lights for gauges
    – charging / coils / ignitors

    I removed:
    – turn signals
    – horn
    – clutch safety switch
    – neutral safety switch
    – dummy lights

  20. admin says:

    oh… my headlight is an aftermarket H4 bulb from pep boys.
    It’s the average normal H4… not the crazy bright blue H4.
    That shouldn’t make a difference… should it?

  21. Emphor says:

    I bought a 81 cb750 from a guy who was having this problem with the bike for a long time. He had several of these fail, but he seems to have eventually found that a rebuilt unit worked better than aftermarket. I never had a problem with it. Good luck…

  22. Bob says:

    All the H4 bulbs I’ve seen at pepboys have been 55W/65W. Old charging systems like this can’t handle that much wattage, it eats them up. You need a 35W/35W H4 which can be found at cycle specific part stores for the same price. I know dime city cycles has them because that’s where I’m getting mine. I’d try that first, it’s the easiest fix (if in fact youre using the higher wattage bulb).


  23. ed says:

    I didn’t know that. Good input. I’ll try that out.

  24. Bob beat me to it! Good advice.

    H4 is just a form factor (size, type, configuration) and does not denote wattage. They come anywhere from 35W up to 140W or so.


  25. ed says:

    yea… good input guys. I’m ordering that H4 bulb from Dime City now.
    Here’s the link if anyone else wants it:

  26. ed says:

    I still think heat has something to do with this issue of the rotor shitting out.
    Everything I’ve previously read says one of the contributing factors is heat.

    Read this… half way down the page:

  27. Yes, it is heat. Where does heat come from in a conductor? Too much current or too high resistance (technically, these are the same. . . as the capacity to pass current is exceeded, resistance ensues).


  28. Jay Felicetty says:

    Does anyone know of someone venting the cover to let the heat out?

  29. admin says:

    nope. not that i’ve ever seen.

  30. Dana says:

    BIG FUCKING THANK YOU BOB AND ED!!! I replaced the rotor and regulator (both were bad), and the bike was charging, but not enough. Read this blog and it hit me between the eyes! The 35 watt bulb was the final piece of my charging problem!!! Got the bulb in the mail today and everything is now peaches and cream for my ’82 CB650!!! Working great!

  31. Pete says:

    I just picked up a 79 650, dude said “all it needs is a battery” hahaha ya ok…. So me being green to bikes said must be good I just saw it run.Slapped a new battery in and ran a few laps around the block. Still good. Hop on roll about 5 min. On my way to work and BAM electrical failure ensues like a bad dream.Thank humans for the world wide web cause if this was pre web I would be knee deep in shit in the dark with out a match! Thanks for getting all this info together its gonna make things a lot easier for me.

  32. JD says:

    I got this same fucking problem again. mine is all rigged it appears as my regulator has survived many bad rotors. three actually. but now i just put in my 4th rotor and the fecker is not charging. i just dont know what to do. my regulator only has 3 yellow and 1 black wire. can someone take a picture of that book up above but turn the page once?

  33. De Waal Visser says:

    Howzit from South Africa,
    really dig the website you guys have got going.I bought myself a ’82 CB 650 a month back,and I have the same problem as you,the charging issue.I took it to the shop today to have it fixed,and the old guy said it looks like it might be the stator.How has your problem been after you changed to the 4-in-1 pipe? does that seem to help ? I don’t think I’ll be able to afford taking it in for repairs every year for this problem.
    Any help will begreatly appreciated,
    Take it easy,
    De Waal

  34. Ed says:

    Hey De,
    I’m not positive if switching to a 4-1 exhaust is the answer… But it could definitely help. Try using the lower amp headlight bulb as outlined in the post.

  35. Matt says:

    I purchased an ’82 CB 650 in 2006. After reading the above, I relived every stranded moment on the road. After a few years of throwing the same parts at it, I decided to wait to fix it. I am now eager to take on the project and proceed with the headlight trick. I just wanted to jump on here and say thanks for all of your hard work and determination!

    I will follow-up with you all as soon as I the project is complete!



  36. Will says:

    Hot dang, this is great stuff. Have been chasing this problem for months. I’m about to get a meter on my rotor, and expect I’ll be ordering a new rotor, reg/rec, and 35W lamp.

  37. Tristan says:

    Having the exact same problem right now, thank you so much for the post. What size of gear/flywheel puller do you need for removing the rotor?

  38. Andy says:

    Hey there Ed,

    Really pants question but which Haynes maual are you using?
    I’ve this version, ( http://www.haynes.com/products/productID/499 ) but page 222 doesn’t exist and I’d really appreciate the steps you’ve got for reference. Thanks for a wicked tutorial anyhow though, I’m just in the process of removing my rotor so really appreciate the help!



  39. Ted says:

    Hi All,

    Here is the problem – it’s the crap rebuilt rotors. With all rotors they use magnet wire. Most rebuilders use plain old magnet wire that has standard Formvar insulation on it. This is good for 105 degrees C, AKA 221 Farenheit.

    That is just good enough to last a year than shit out. Honda speced wire with better insulation when it had OEM’s make these rotors, but your not going to find one of these brand new unless the Gods of NOS can find one in a warehouse somewhere and even then it’s going to require your first born, all your money, and sacrificing a goat on an altar at midnight.

    They make magnet wire that has Polymide insulation good up to 250 C AKA 480 F but it’s more expensive so your average motorcycle rotor rebuilder isn’t going to use it – after all they want your rotor to crap out so you buy another one.

    You can rewind your own rotor you just need an arbor press to separate the halves. Just wind on the same size and amount of wire. And buy decent wire. Or find an alternator rebuild shop to do it. Or go back to your regular rebuilder and threaten to tear his fucking head off if he uses the standard crap wire.

    Here’s an insulation table:


    More info on it:


    Good luck! I sent my last rotor to a guy in Alabama who rewinds these, we’ll see how well it works out.

  40. […] and dying just 10 minutes into a cross-town trip last week, and she's still parked. I suspect a damaged rotor. Replacing the rotor will be my first real bit of mechanical work… ever. (Some chain maintenance […]

  41. greg arnold says:

    I fixed that problem. The problem is, everything in that alternator housing gets cooked because there is no way it can keep cool. I got a peice of stainless steel and made a small air scoop to fit on top of the housing. Under the scoop I drilled 3 x 5/16 holes to let air in. Under the bottom of the housing I drilled another 3 x 5/16 holes to let the air and any water out. I have now done 45,000 kilometers without a problem. I polished the stainless steel and it matches the polished aluminium.

  42. Mycroft says:

    @greg arnold, How did you attach the scoop? I was thinking about machining some slots at the mating surface of the housing to the case to enhance airflow, but like this idea as well.

  43. gary gee says:

    @greg arnold, Did you drill these holes into the case, or into the removable cover? Also, did you drill them at the very top, or at about 10 or 11 o’clock? Also, the holes you drilled on the bottom are at the very bottom, or are they slightly to the rear of the very bottom? Can you send a couple of pictures? Here’s my email address: garygood1a@att.net

  44. Beth K says:

    I like this vented idea. Could you also send me pics? Thx Beth idigahorsie@gmail.com

  45. Max says:

    Hey all good info here! I want to help keep it alive!

    Mine: 79 cb650, mac 4 to 1, jetted 45 low 120 mains 1100 altitude (Minnesota).

    Kept all lights replaced with low led. All is well then bam charging issues. Rotorlooks solid, stator needs a cleaning, but the rectifyer…good god. Looks like some one melted candels all over it. Headed to the junk yard tomorrow for a cheap fix.

    Nod to the scoop idea, as I was reading I kept thinking why not just tap a few air holes?

    Any final thoughts on the 35w bulb or the meter? People seemed excited about it just looking for a final ya or nay.

  46. eduardo muller says:

    I like this vented idea. Could you also send me pics? Thx

  47. Brad J says:

    For those removing the rotor and dont have a gear puller.. I seen a trick on YouTube where a guy unscrews the rotor nut and threads the rear axle in. He taps it with a hammer a few times after that and presto.. The rotor comes right off. No gear puller required. Tbis was for an 81 cb650 custom

  48. Lorenzo says:

    Hi All…

    It seems that I’ve got the same problem. No one has an image of the air scoop?


  49. Federico says:

    @greg arnold Sorry for bothering you,
    I was reading about the air scoop for the Honda CB 650 rotor. Do you have a photo of how the scoop is made?
    Thanks a lot for the help!! federicobarazzoni@gmail.com

  50. C.Rama murthy says:

    Your problem basically may be too much heat being generated internally in the rotor’s electromagnet. Your work of moving exhaust pipe away removes any doubt of the hot air blast heating this up.You can calculate the amount of electrical power dissipated in the rotor circuit’s resistance of 4 to 6 Ohms.It is VXV/R or 13.6X13.6/6 approximately 31W, dissipated as heat.In other words you have a hermetically sealed 31W heater in your rotor continuously heating it up. You can confirm this by measuring its temperature soon after a long ride.In that case, you have to reduce the rotor current while maintaining the ampere turns balance so that the magnetic field generated will not be reduced. This can be achieved by rewinding your rotor by a thinner wire(more turns), which increases the resistance, reducing the dissipated power.Some alternators have a way of regulating the voltage by reducing the field current by electronic circuitry which results in a constant 13.6V despite increasing speed and increasing (unregulated)alternator voltage. In case you are aware of such a control scheme,reducing the field current by adjusting the setting in electronics may be a possible option. An expert who knows about the regulating mechanism (if it is not potted) can help. If rewinding is not possible, you should plan to couple the heat generated in the copper wire to the case, say by smearing some heat conducting adhesive, which holds the wires and also conducts away the heat, improving the situation.I am no expert in these vehicles but just know a bit about electrical aspects and thought letting you know the source may help you solve it in a better way if the issue still exists.

  51. jason says:

    I’m glad to see this thread stay alive over the years; I mean–glad as I could be for any of us fighting with our cbs. I’ve experienced every facet of electrical nightmare described herein with my ’82. I’ve replaced every component, too. Thanks for the bulb link. Also, I found a replica wire harness on partsnmore, and I’m going to give that a shot…just because shit gets old. Anyone have any experience with this harness (part # 73-0930)?

  52. Max says:

    Hey all checking back in. Well its been a ride. Stripped down rebuilt, measured and installed new seals a 79 cb 650. Re-jetted, pod carbed, 4 to 1 Mac. HAND TUNED LIKED A BOSS.

    Enter in The electrical problems… Replaced the entire charging system, sometimes I can get out and back no problem other times it just dies. Readings are 4-6 on the rotor, battery tests good, new stator and rectifier. Enter in the head light, and removal of the blinkers.

    Wanted to mention about the venting of the rotor, there is an oil plug in side of there and obviously you’re not going to want to get dirt and grime in there.

    One thing that is not mentioned here that I have done is the additional oil cooler, which helps knock down the temp by about 30-50 degrees depending on the free air temp. Here is a nice little walk through on another great site: https://www.chinonthetank.com/2010/07/lockhart-oil-cooler/

    Oh! Lastly YES you can just use the rear axle as a puller for the rotor. It’s legit and worked on my cb650 79’ here is a link: https://www.youtube.com/watch?v=yVU_RUE0c4o

    Good luck to you all!

  53. John says:

    I have an 82 650 Nighthawk with electric charging issues, stator tests at .6 ohm between yellow wires and book says SB .3 to .4 ohm, it appears I need a stator? Vrr and rotor test good. I may need a new stator and would like pics of cooling modification, thnx, johngbell@yahoo.com

  54. John says:

    My mistake, book says .4-.5 ohm between yellow wires to stator, i measure .6 ohm on mine, what’s da verdict? Rotor, vrr test OK. I can’t get my 14-15 volts at 4k on tach. Ideas? Best source for a stator, if I need? I’m in SV AZ, 85635.

  55. Roger says:

    I have a 1979 CB750. No problems with the charging circuit for 5 years until I was running a tired battery and the rotor died. Changed the rotor and then died again after one year. Everything ohms ok but no charge. Could RPM in addition to heat be a cause for early failure? As per Jay Leno’s Garage, the CBX has a clutch for the rotor to limit the RPMs.

  56. chis says:

    fought this same problem for 2 years. this charging system from cycle exchanged fixed it.


  57. Rob says:

    Did everyone know that a Yamaha xs650 rotor fits cb650, and they usually cheaper

  58. […] 79-82 Honda cb650 charging problems – Chin on the Tank … Ok… this is where it gets tricky. The main thing that will go wrong with the charging system is the rotor. There are 2 different ways that the rotor will shit out: […]

  59. Reuben says:

    Thanks for posting this..these are the same charging problems i face on my 81 cb900f. It was hard finding a new rotor here in Kenya so i had mine redone,works perfectly but once in awhile something will come off inside the casing n snap the wires its either that or if you run the bike with the headlamp on the batt gets drained especially at low rpm..so most of the time i make sure everything is off unless am on a night ride bt still the original sealedbeam headlamp doesnt illuminate much as you have to be at high rpms to keep it bright so will also be changing that . I also recently noticed that my bike is having a hard time starting up once the bike heats up like the batt is drained meaning there is minimal or no chargin when heating occurs (could it also be a sign of a dying batt that needs replacing maybe?). Very helpfull with the vent idea thanks as i will sort the heating issue on the rotor side now.

  60. Steven O says:

    How do I know which one of these to replace? the rotor, reg/rectifier, stator, or headlight bulb? 80 CB650

  61. Great thread! To reduce heat build-up.. Has anybody tried switching out the unventilated alternator cover with a ventilated cover from a 1983 650sc?

  62. Cosmin says:

    Guys. I just finished my cb 650 ‘79 and i got my battery dead. There is a clear solution that works at someone and last ?


  63. Shay Maoz says:

    This is one of the very interesting conversation. it is keeping alive over the years.
    i own a Honda 1983 CB550sc, of course with electric problem. battery is not charged. once again, the stator looks damaged. it is so hard to find this peace, till i did found the following one who is manufacturing this parts.
    hope it will help someone.

  64. Trinity says:

    I have a 1981 Honda CB650C and having same issues, going to replace the 3 parts and check my headlight. If that doesn’t work I will resort to the vent idea i just hope someone posts a picture so I can see 😂

  65. John M Cox says:

    Im not an electrical engineer but I konw that electrical resistance increases with heat. Heat is everything. An air scoop mounted somewhere else with a chamber and filter to filter out water and bugs would be prudent. Then a new rubber tube leading down to the cover. It would need a vent hold as well and the bottom of the cover is the logical place. I have a 1980 cb650c and have been considering this, have come back to this post many times over the years.

  66. William Davis says:

    Wow, it looks like everyone with one of these has the same issue I do. Has anyone tried to use an LED light that runs LESS than 35 watts? They are super bright, and should use closer to 5-10 watts, maybe even less depending on the light. I have even considered (am still actively considering) adding solar someplace to try to take some load off the charging system, adding another battery someplace to assist with getting stuck and reduce the likelihood it gets low before I plug in the maintainer at home, I see someone else thought of ventilation and I have some marine clamshells I could install on the case to ventilate. These are shaped like scoops and are in stainless steel. I got them on Amazon for my boat. This is a major issue because I get 6 months to a year then the VRR craps the sheets. Consistently. I bet the charging system is killing it.. This bike is a blast to ride, but she loses a lot of shine due to this electrical issue and how often she leaves me walking down the road. Speaking of which, does anyone notice their bike being damned hard to push even with all new wheel bearings and brake system? Mine is like pushing a car in neutral with a sticking brake…

  67. Erik says:

    Power consumption is an important component. I renewed the rotor stator regulator and the battery, and still it drained the battery after 1-2 hours of driving. Ground cable, + cable renewed was of no use. The problem ended up being the wiring from the taillights. There are so many bad plugs … everything renewed, drove 6 hours today, city, country … arrived at home 13 V open circuit voltage (AGM battery) Also check your plugs, best of all and renew all plugs at the back of the light. The crimps were also bad there.

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From Past

Published - Aug 27, 2012

Full Tilt Motorcycle show – photos

Big thanks goes out to our friends at Works Engineering for hosting all of us this past weekend. Great time for sure! Click HERE to see all the PHOTOS.