Results 1 to 6 of 6
  1. #1

    79 750K Battery Won't Charge

    I got a new to me 750k that has a couple issues. The big one I want to tackle this week is a lack of charging. Leave the bike on the tender over night and it makes it about 15 minutes before it starts misfiring and ultimately dies with no power, ignition, or lights. The bike starts immediately after a battery charge and idles surprisingly smooth (I'm so used to gummed up, been sitting carbs).

    Possible issues:
    Check battery cold and under load with voltm
    Rotor?
    Coil wires?
    Harness?
    Rectifier?

    I'll check the battery and rule it out and then move on to what this forum seems to point to as the usual culprit, the rotor. Question is- is there a way to test it before ordering one?

    Sent from my Pixel 2 XL using Tapatalk

  2. #2
    CB750 Addict Dave's Avatar
    Join Date
    Sep 2012
    Location
    Ca
    Posts
    497
    A tender is not going to fully recharge a dead battery. You need to put it on a real charger.

    Obviously it's not charging or it would stay running.

    Honda 1979 thru 83 CB750 Service Manual Chapter 16 Battery Charging System.pdf
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  3. #3
    Thanks Dave. I got the factory manual from my the PO and started from the top.

    Battery out the battery reads 12.8 volts

    Running with the choke at 2k the bike reads 12.40 and gets to 12.55 at 3500k.

    I disconnected the rotor power and popped the case and a bunch of stuff fell out and it smells awful. Pics below.

    All yellow cables have continuity and none have continuity with ground. I noticed that the the coil does not slide over the rotor without resistance- could it be rubbing?

    The brush scribe lines seem to have some distance to the ends.

    My gut reaction is the coil is good, but the rotor is rubbing or coming apart and needs replacement, but is it possible that the rotor is spinning on a bent surface?

    Sent from my Pixel 2 XL using Tapatalk

  4. #4
    CB750 Addict Dave's Avatar
    Join Date
    Sep 2012
    Location
    Ca
    Posts
    497
    WTF is that yellow stuff in the rotor? That's not supposed to be there.

    On page 16-7 you see "specific resistance". You need to check that with a decent ohmmeter. Simple "continuity" is the same as a short. Later on in the chapter you'll need that ohmmeter quite often.

    I'd replace that rotor, it's not supposed to look like that.

    Click image for larger version. 

Name:	Capture.JPG 
Views:	2 
Size:	36.0 KB 
ID:	8485
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  5. #5
    Thank you Dave. Are the Rick's rotors worth it or should I spring for an OEM? I see electrosports has a much less expensive unit but if their Vstrom reputation is anything to go by I'm already not trusting.

    Sent from my Pixel 2 XL using Tapatalk

  6. #6
    CB750 Addict Dave's Avatar
    Join Date
    Sep 2012
    Location
    Ca
    Posts
    497
    I've never had to buy one myself.
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

Similar Threads

  1. Low charge voltage
    By Cbjoe82 in forum Electrical
    Replies: 26
    Last Post: 03-16-2018, 05:40 PM
  2. 1979 CB750 wont charge
    By cbtdc in forum The DOHC Garage (1979-1983)
    Replies: 9
    Last Post: 06-06-2017, 08:24 PM
  3. New stator new flywheel bike still will not charge
    By 80cafe750 in forum Electrical
    Replies: 0
    Last Post: 11-14-2015, 06:07 PM
  4. 80 750c upgrade charge system
    By mlbjb16 in forum Electrical
    Replies: 6
    Last Post: 09-11-2015, 05:32 AM
  5. Battery not holding charge!
    By Jose in forum Electrical
    Replies: 2
    Last Post: 09-09-2015, 02:40 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •