collapse

www.dimecitycycles.com


www.restocycle.com

www.CITYLIMITMOTO.com

www.jadusmotorcycleparts.com

www.bisonmotorsports.com

www.speedmotoco.com

www.cognitomoto.com

www.townmoto.com

www.sparckmoto.com

www.Moto-Madness.com

www.pistonsociety.com

www.steeltowngarage.com

QUESTIONS ABOUT THE SITE? TROUBLE REGISTERING? ADMIN@DOTHETON.COM

Author Topic: '80 CB750F Electrical Issues  (Read 903 times)

Re: '80 CB750F Electrical Issues
« Reply #10 on: Aug 30, 2017, 10:00:06 »
cxman,

Yes, I'm now realizing I started at the wrong end of the system. lol This is my first CB, so I'm sort of learning as I go. Guess I won't have to worry about charging issues ever again!

Offline cxman

  • DTT SUPPORTER
  • *
  • Posts: 2336
Re: '80 CB750F Electrical Issues
« Reply #11 on: Aug 31, 2017, 20:16:13 »
the rotors cook from heat and no ventilation

 
1978 CX650 Super Deluxe
1979 XS1100 Special
1974 xl350
1983 cx650 Custom
1973 cb750
1980 cb750
1981 cb650
1982 cb900 c
1974 kawasaki 350 bighorn
1983 GL1100 aspy full dress
1983 GL1100 Nekid
and a bunch of others

Re: '80 CB750F Electrical Issues
« Reply #12 on: Sep 11, 2017, 12:47:55 »
Okay, so I installed the rotor and new brushes. The bike seemed to be holding a charge, so I rode it 100 miles yesterday, checking the battery every 20 or so. I had 12.5 volts, consistently, at each stop (ignition off), but when I got it home, it was reading 10.5 volts and couldn't even turn the starter.... I'm quite stumped at this point. The entire charging system is brand new, and it rode perfectly for 80 miles before the battery started draining.

I did notice that there is a small rectifier on the wiring diagram that connects the clutch switch, neutral switch, and starter solenoid(?), but that's the only thing left that I can possibly think to replace at this point...   >:(

Any ideas, gentlemen? I'm starting to think I need to just take it over to the stealership.

Offline Sonreir

  • Moderator
  • DTT SUPPORTER
  • *
  • Posts: 10307
  • Oregon
Re: '80 CB750F Electrical Issues
« Reply #13 on: Sep 11, 2017, 12:54:54 »
The charging system shouldn't be too tricky to test. You have your multimeter handy?

Start at the battery and work our way back.

1.) With the bike idling, measure voltage across the battery terminals. It should be in the low 13s, but anything over 12.5 will suffice. Give it some revs and you should see the voltage increase up to 14.5 max.

No change when revving? On to the next test.

2.) Switch the multimeter to read AC instead of DC. Check between each of the yellow wires going from the alternator to the regulator/rectifier. You should see somewhere between 20V and 40V.

No voltage? Time for the next test.

3a.) Switch back to DC voltage and check the black wire running from the regulator/rectifier over to the alternator. You should get 12V on this one.

No voltage? Check the black wire going into the regulator/rectifier from the harness. You should have 12V on this one, too.

3b.) Next, check the white wire coming back from the alternator to the regulator/rectifier. This wire should also have 12V.

If no voltage on this one, you have an issue with the rotor and/or brushes.
Sparck Moto - http://www.sparckmoto.com

Audaces fortuna iuvat.

1977 Honda CJ360 - Café SOS - Stage One™, Café SOS - Stage Two™
1976 Puch Maxi - APuchalypse Now
Suzi T500 Cobra Resto

Custom Gauge Graphics
Custom Wiring Harnesses

DTT Red, White, and/or Black 360 Club - Better than those Blue guys

Offline cxman

  • DTT SUPPORTER
  • *
  • Posts: 2336
Re: '80 CB750F Electrical Issues
« Reply #14 on: Sep 11, 2017, 21:24:52 »
did you do a resistance test on any of this ?

rotor ohm test stator test

wiring continuity test

battery test
1978 CX650 Super Deluxe
1979 XS1100 Special
1974 xl350
1983 cx650 Custom
1973 cb750
1980 cb750
1981 cb650
1982 cb900 c
1974 kawasaki 350 bighorn
1983 GL1100 aspy full dress
1983 GL1100 Nekid
and a bunch of others

Offline esmoojee

  • Posts: 165
Re: '80 CB750F Electrical Issues
« Reply #15 on: Sep 12, 2017, 01:45:17 »
Get a cycle x charging system and you won’t have any of these problems.  Mine provides a consistent charge while riding and idle. I get easily 12.5 or higher at idle The charging systems on the dohc were not great as already stated. You could have a bad battery as well. I'd take it and have a load test done at the auto parts store. 

Offline ChopperCharles

  • Posts: 56
    • Modified Motorcycles by Chopper Charles
Re: '80 CB750F Electrical Issues
« Reply #16 on: Sep 12, 2017, 11:56:35 »
Even with a new rotor, the charging system in the DOHC is abysmal. It will. not. charge. at. idle. Period. If you're in stop-and-go traffic, you will eventually run out of battery. I replaced the rotor and regulator in my 1982 CB750C, then I re-wired the charging system with 12ga wire, just to be overkill. Still didn't do it. Changed all my turn signal and tail light bulbs to LED -- even the gauge cluster bulbs. Still just barely above 12v at idle. At 3000rpm it was charging fine. Eventually bumped my idle up to  ~1600rpm and that was just barely acceptable. If I had kept the bike, my next step was to find a Euro style left handlebar control, which allows the headlight to be turned off.

I loved my CB750C, but damn that charging system. Damn it to hell!

Charles.

Re: '80 CB750F Electrical Issues
« Reply #17 on: Sep 12, 2017, 12:40:40 »
ChopperCharles,

The more I read, the more it sounds like I'm always going to have this issue, even if I do get the system running "properly". I've been trying to keep the revs at 3500 and above when riding it, but that's only feasible for so long... Now, if I were to go out and trade up to a CB900F, or (dare I say it?) a CB1100F, would I still be encountering these same charging issues, or do those bikes have a better system?

Offline Sonreir

  • Moderator
  • DTT SUPPORTER
  • *
  • Posts: 10307
  • Oregon
Re: '80 CB750F Electrical Issues
« Reply #18 on: Sep 12, 2017, 12:41:58 »
The charging system is the same for all the 80s DOHC Hondas.

That said, how are you not keeping the revs above 3500 when you're riding? Unless you're idling for really long periods of time, all riding is usually done at like 5K or more.
Sparck Moto - http://www.sparckmoto.com

Audaces fortuna iuvat.

1977 Honda CJ360 - Café SOS - Stage One™, Café SOS - Stage Two™
1976 Puch Maxi - APuchalypse Now
Suzi T500 Cobra Resto

Custom Gauge Graphics
Custom Wiring Harnesses

DTT Red, White, and/or Black 360 Club - Better than those Blue guys

Re: '80 CB750F Electrical Issues
« Reply #19 on: Sep 12, 2017, 12:45:00 »
Sonrier,

Let me clarify... What I mean is that I keep the tach over 3500 even at low speed (i.e. 15-30mph). Anything above that, I'm definitely cruising in the 5-6K range.