Topic: 1976 CB750K going through headlights like tissues!

[Beatmalls]

Hey SOHC4!

I am a bit stuck on an issue - well more like I'm not sure where to start - and I'm hoping someone might have some tips to get me on the right track.

Basically my bike is burning out headlights over and over.  Well, I've gone through two in as many months.  One burnt out after years, so I got a replacement, then that one went in about a month.  At first I thought I might have just got a bum unit so I picked up another, but THAT one just went out, so it seems pretty clear something is up with my wiring..

It's a stock setup (as far as I know), not LED or anything, and the bulbs I've been burning out have been Wagner Lighting OEM Replacement Sealed Beam Headlights.  It's the same sort that worked fine for a good long time though so I'm thinking it's not the bulb itself.

I've poked through the electrics FAQ it's pretty general (and I'm not the most adept at the electrical side of things).  I'm hoping I will be able to get to the bottom of this specific issue more quickly with a few tips from you ultra-knowledgeable people!  Really I just want to know what are some likely candidates for this issue (is it a short?), and maybe some tips and for diagnosing the source of this issue, like what to look for, where to stick the multimeter.. or anything that might just get me started.

Anyway I am open to any suggestions as to where to get started, ideas large and small welcome.  Thanks for listening!

~Shane

[rodsragsnrides]

what is it charging at? You are aware the stock regulator is adjustable(voltage),it's likely overcharging from your description

[Beatmalls]

Aha - overcharging? ok!  I'll look into that   And no, I had no idea, so thanks already.

It's late so I can't start the bike up without waking the neighbors so meantime I'm going to RTFM about the charging system and look at my regulator.  Thanks for the insta-tip!

~s

[754]

Car headlites have weaker filaments than motorcycle seal beams... They have heavy duty version.

[ekpent]

  Seems like if you had a real high electrical spike the fuse would blow. May want to see what is in there also while your poking around.

[rotortiller]

You have poor quality bulbs, vibration or voltage issues.

[Beatmalls]

  Seems like if you had a real high electrical spike the fuse would blow. May want to see what is in there also while your poking around.

Yes I actually have blown a fuse recently!  Two actually, different timing than the headlamp but that'd be another indicator that the regulator is the culprit.

I cracked the panel off to have a look because I know the PO replaced the regulator/rectifier (5+ years ago) with something that's non-stock, but it does appear to be adjustable.  Still no time to test it out so I'm not sure what it's charging at just yet.

[flybox1]

Thats an oregon motorcycle parts vreg.  A good unit, but typically purchased as a bandaid to cover the real issue 

[Beatmalls]

Oh really, color me interested - What sort of issue would it be used to cover up?

[flybox1]

Electrical is not my forte.    Hopefully you will get more input from Scottly, calj n others....
Increased resistance throughout the whole harness and the OEM Vregs inability to properly maintain a battery are two issue that come to mind.

[b52bombardier1]

Get a good multimeter and measure the AC volts and DC volts at the battery with the bike running at half throttle.  Hope for around 14.5 vdc and less than .1 volts AC.

This will tell you if it's overcharging.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[Beatmalls]

Had a chance to nip down and test it out - was passing 15.5v when up to 5k rpm. 

I fiddled with the adjuster (which works opposite of what I'd think) it and now it's about 14.5 give or take .1v.  Will pop a new lamp in there and hopefully that'll be that.

Thanks everyone for the guidance, as always, you are the best, most helpful community out there!

~Shane

[b52bombardier1]

What did your meter indicate for AC volts?

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[Beatmalls]

Alrighty I was unsure about the AC measurement - so after your response I went and dug up the manual to be sure I was reading it correctly.  Now I'm sure I've got it set up right but I'm still not sure about because from what I can tell, I'm reading a 26 on the meter when it's idle, and 30 when it's up to 5k.. what the heck could be going on?  Am I just reading it incorrectly, like it's a decimal place off?  My multimeter is a BG instruments GDT-11.  The options for AC volts is 200 or 500.  On both settings it's showing 26-30.  Hrm..

[flybox1]

At 3500rpm set it for max 14.4v-14.5v.  It should never go higher than that.

[b52bombardier1]

My Fluke meter is auto ranging so it's a no brainer for me on AC volts  measurements. I would connect your multimeter to a known AC value such as 120 volt AC house electricity (if it can handle this much power) so that you can resolve the bike number on your meters display.

But if it is that high on AC, your rectifier is shot and you will soon kill your battery.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[Beatmalls]

Oh of course, that makes sense!

Tested it a few AC sockets and yep, it's reading 120.  So my rectifier is shot then you say?

Tested out the rectifier and it actually looks like it checks out fine - continuity in one direction, not in the other.  Hrm..

I am wondering, if it is the regulator or rectifier, would it be an upgrade at all to get a combined regulator/rectifier?

[scottly]

Electrical is not my forte.    Hopefully you will get more input from Scottly,
Increased resistance throughout the whole harness and the OEM Vregs inability to properly maintain a battery are two issue that come to mind.

Beatmalls, place one meter lead on the battery + post, and the other one on the regulator black wire, while still connected to the reg, and read the voltage with the key on. If it it more than 1 volt, there is too much resistance somewhere in the path from the fuse box through the ignition and back to the reg.
I'm guessing that the AC readings you got were directly at the stator leads, disconnected from the rectifier. If so, they are normal. The symptoms of a faulty rectifier are undercharging, not over-charging, so your rectifier is fine.

[Beatmalls]

Ahh, oh really - I was indeed reading it incorrectly then!  I was reading from the +- of the battery terminals - I wasn't so sure but  the wording in the shop manual is just a bit cryptic, thanks for the clarity.  I'll test it out tomorrow as you describe, thanks for the input!

As an aside - it was fun to pull off the rectifier and test it out at least .  I am learning a lot with all this fumbling about.

[scottly]

Just to clarify: The charging voltage of 14.5 is read across the +- battery terminals, but the voltage drop to the regulator is read from the battery + to the black regulator wire. This is what flybox was talking about when he mentioned that adjusting the regulator may have been a band-aid that covered the real issue. Do the voltage drop measurement, and report back.

[b52bombardier1]

The idea here was to test how much AC was leaking past the rectifier to reach the battery posts.  This test had nothing to do with testing how much AC was coming out of the stator - don't care at this point. Testing stator output would be important if he was undercharging but that's not the case here.

   My suggestion above is a quite simple, non-invasive test that only requires the removal of the battery side cover and a decent quality multimeter. If he had an auto ranging multimeter for display scaling, it would be even easier. My Fluke model 17B multimeter fits this requirement perfectly.

Rick

[Beatmalls]

thought I'd posted this last night:

Ahh so I wasn't testing it properly, thanks for the clarity!  I was testing between battery terminals. 

I'll test it as you describe, from battery + to black regulator wire and see what it reads.  Left my multimeter at home today so I'll have to check it out tonight. 

Thanks for the clarity!

~S