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Hey guys so I've lurking about the site for a while reading and learning. I'm not new to the auto scene by any means but this bike is giving me a run for my money.
This basket case just doesnt seem to want to charge. The bike is a 81 Honda CB750..and I have replaced just about every electrical component on this thing and it still wont charge. Stated with replacing the rec/reg with a confirmed working one, still no good. Next i replaced the stator with again working one. Still no dice. Also I've made sure all the ground are good.
I'm getting close to selling the bike bc it is annoying me so much. Anyone that could chime in with any info would greatly be appreciated.
In the Service and Parts Manual section here on DTT I posted links to the factory service manual for our DOHC CB750's. http://www.dotheton.com/forum/index.php?topic=44399.0
There you will find the electrical section for the CB100C, much better troubleshooting and specs were given in that manual and they directly apply to the CB750's.
You do have a volt ohm meter right? Not just using the SWAG method.
Thank your for posting those manuals. But yes I have been using it like crazy chasing wires and grounds. Yes sir i sure do have a volt/ohm meter. with the meter hooked up it doesnt seem to ever pull more the 12.5-13v at more then 3/4 throttle.
It could be your battery. What's the condition of your rotor?
But seriously, have you considered just taking it to a shop to get fixed? Selling the bike because you can't figure out an electrical problem seems a lot like throwing the baby out with the bath water.
HAHA thats a pretty good analogy. Dont worry I'm not gonna sell it just because of this..If anything it would annoy me even more that I never figured it out. The battery was new as of the winter..I wanta say January. Well I decided to give the battery a nice long charge so i put it on the trickle charger for 2days. After that I checked and the battery and its sitting at 11v. I guess running it dead the 3+ times just hammered the cheap Walmart battery. So I just picked up another battery today. And its on charge for the night. I will report back tomorrow if anything changes.
HAHA thats a pretty good analogy. Dont worry I'm not gonna sell it just because of this..If anything it would annoy me even more that I never figured it out. The battery was new as of the winter..I wanta say January. Well I decided to give the battery a nice long charge so i put it on the trickle charger for 2days. After that I checked and the battery and its sitting at 11v. I guess running it dead the 3+ times just hammered the cheap Walmart battery. So I just picked up another battery today. And its on charge for the night. I will report back tomorrow if anything changes.
Lead/acid batteries HATE to be run dead, and it permanently damages them to be left in a discharged state for any length of time.
Make sure your "trickle charger" is an automatic battery maintainer. A so-called "trickle charger" will slowly cook a motorcycle battery. A Battery Tender or equivalent float charger is what is needed. You can leave a battery on a float charger indefinitely without damage. Good idea to hook your battery to it any time you are not using the bike.
Good to know about the trickle charger. Mine is a float charger though.
Well Battery was nice and charged this morning so I hooked everything up, still not charging.
Alpha you mentioned something about what shape the rotor is in? How would you know what shape it should be in? When I energize it the magnet seems to be strong as hell.
Haha ok kinda what I figured. Ugh I'm like out of things to try at this point.
I have found that my ignition switch is on her way out. Sometimes it will not have parklights, but it never caused the bike to shut down or not start though. Not sure if this could be a related problem or not. But honestly I have nothing else left that i can think of.
I take it you have checked out the rotor, rotor brushes, field coil, RR and the battery as shown in the manual HD gave the link too and they all checked out OK
If all those checked out OK I admit I'm stumped as to what it could be.
connections between the checked parts can be bad, also check behind the fusebox, where the wires are attached. residu builds up there and will kill any current.
connections between the checked parts can be bad, also check behind the fusebox, where the wires are attached. residu builds up there and will kill any current.
I have clean just about every connection I could find on the bike and sprayed them all with wd40 before re plugging them together. But good call on behind the fuse box. Actually on that note some one added a wire with a fuse where the main fuse should be. I never thought anything of it because its a heavy gauge wire with a 30amp fuse. Think that could case anything.
hi,
i see no mention of the field coil and circuit...ck the f/c at the connector and then at the actual brush connection it should be the same, if nothing then check the actual rotor readings with the brush holder removed . readings per m/m . with all components assembled including the alternator assembly and cover turn the bike on and off(key) while holding a hacksaw blade between your thumb and finger (lightly) vertically close to but not touching the case. when power is turned on the blade should be attracted to the magnetic field telling you the field is operating ok statically. you can also test alternator a/c output, about 60volts between legs at 5k (approximately)..
joe@vcycle
www.joesvcycle.net
www.joesvcycle.wordpress.com , shop technical tips
Ok so I was doing some more tests. This time I isolated the rotor. When I checked the continuity across the 2 copper bands it only comes to .8 I'm guessing this isn't good. I also did the saw blade test and couldn't feel any pulled from the side of the case.
o.8 ohms is not good. Should be between 3 and 5 ohms. You do need to clean up the face so you have clean copper and push the probes very hard into the ring as well. But if the magnetism test is failing its probably shot anyhow.
What output are you getting out the generator? should be 8-15 Volts AC across any two of the three yellow wires.
Hey guys just an update. I found a guy selling a whole DOHC 750 motor with the electrical harness for 100bucks. Jumped on that deal.
So I check the resistance across the copper bands of the rotor 4.4 ;D so I put it on my motor. Hooked the volt meter up fired the bike up low 12v still. This made me want to almost push the bike into traffic lol.
Then I figured for the hell of it the other motor also has a R/R so I wired that in and I figured while I was there I switched the main fuse block and the starter relay. So after replacing just about the entire electrical system I fire it up again. BOOM 13.7v give it some gas and it goes right up to 14.5v and holds.
So over all I guess it was a combination of things all getting fried together that screwed me.
WHOO-HOO!
Nothing like what I call "The shotgun method" of motorcycle repair. Throw everything you got at it and see what happens.
So now you got another project?
WHOO-HOO!
Nothing like what I call "The shotgun method" of motorcycle repair. Throw everything you got at it and see what happens.
So now you got another project?
HA this bike is still an ongoing project. Im going to make a build thread one of these days. But its kinda of halfway there so i cant say how eventful it will be lol.
But thanks for all the help and info DDT members rock.
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