Topic: The Flickering Headlight Syndrome - At A Loss...

[sugarmcguinn@msn.com]

I'd like to start out by saying Hello!  I'm not new to the forum, but new to posting.  Over the years I've benefited very much from the forum and it's members experiences, knowledge, and in some cases, mistakes ;-).


I'd also like to thank Hondaman.  He has been a savior to me on my projects, with parts (arriving many times before I paid for them), lengthy emails trying to help me solve problems, and knowledge (My CB750 is amazing!)  Thank you Mark.  ;-)

On to it.  Flickering Headlight - I've searched through the archives, and found a few things on the flickering headlight, and Hondaman and I have traded a few emails on the subject...  but I think my issue is proving to be a little left of elusive...  So I thought I'd throw it out to the forum and see if anyone else has run into this and might know of a solution, or course of action....

The Deets: Bought this bike from a friend of my Mom's a few months ago.  Had it in the garage since the late 80s.  Started it every now and again.

1978 CB750 F (stock, save a few Hondaman component upgrades)

Bike doesn't want to run when she's cold.  Needs choked quite a bit to start, but runs and idles fine after warm up (needs the carb's rebuild and adjusted, I assume- This seems pretty par for the course to me) Charging system is all working within spec (I've tested it myself).   regulator and rectifier check out fine (tested these as well).

Headlight comes on with the key, cuts out when starting and lights fine during the warm up...  I know when its warmed up, because the headlight starts flickering on my garage wall
This is completely isolated to the headlight, as far as I can tell.  The other lights seem to work as they should.  And there is no noticeable difference in the way the engine is running...

Hondaman advised me on the high-beam/low-beam filament issue that can cause the headlight to flicker. So I hooked up the headlight directly to the battery, left it on for a half hour and shook the shXt out of it.  No flicker....

A thing of note.  I noticed when I got the bike that someone had bypassed the headlight fuse and wired in an inline fuse.  AH!  These CB fuse blocks were terrible were like that.  I ordered the Hondaman Fuse Block, and thought I was good.  upon installing it, the headlight fuse blew immediately. Fluke, i thought.  popped the spare in (which HM so graciously provides with his blocks), it blew as well...  then a popped the old block back in and the head light came on without blowing... I increased the fuse value of the HM until it held. 15 amps (7 amps is what it should have) which, I then noticed) was consistent with the fuse the previous owner had wired inline.

Another thing of note...  While riding the beast with the Club the other night, I noticed that riding around at low RPM the headlight was stable, but as soon as I rolled the throttle on the headlight would flicker, or go out completely.  Then come back on when the bike came back down...

Another, Another thing of note...  While messing around with it in may garage, I swore at one point that I noticed the headlight blinking opposite of the turn signal...  I couldn't make this repeat, and it's not doing it now....  Just thought I'd throw it in...  Maybe I made it up?  But I swear it happened.

 I'm kind of scratching my head here...  Is this just a bad ground somewhere...?  I've checked all the grounds I can get to without pulling the bike apart...  I'm wondering...  Can I test the bad ground theory by running a "new" ground from the headlight socked to a ground (and with a wire) I know to be good?  Does this sound like an indication of the Starter button switch?  Should I just say F-it and replace the whole harness?

Any thoughts are sincerely appreciated. 

Thanks.

Sugar McGuinn

[Jerry Rxman Griffin aka MuthaF'er]

What shape is the headlight socket in? I've seen broken ones.,

[eigenvector]

Mine flickers because the bullet connectors for the plug are crummy.  one more thing for me to follow up on.

[sugarmcguinn@msn.com]

Interesting....

Two things for me to rule out.  Thanks!!

[flybox1]

Power it directly off your battery via a relay.

[Don R]

 I'm big on grounding, bad grounds cause more grief than most other electrical gremlins and yours sounds like an incomplete circuit at times. The easy thing is you can add a ground here and/or there. I usually chassis ground the extra green one at the blinker and run one from green to the frame at the coils if there isn't one already there. too.

 On my race car I use the chassis to ground to but also run external ground wires (like the honda green ones) from lug to lug and also ground the heads to the ground system.  An MSD can fire to the piston top if it has nothing else to ground to. Not likely a Honda ignition can do that, but you get the idea.

[brewsky]

I had similar symptoms, and turned out to be the filament broken in two, but still touching.

Try another headlight?

[Muckinfuss]

In my experience, the following (in no particular order) have contributed to unwanted flicker.....bad filament, bad diodes in rectifier, bad points in non-solid state regulator, bad battery plate(s), crappy ground of a wire that can never be found.  Now, I don't have any science to back this up, but low RPM flicker would cause me to go after the bulb first.  Flicker at high rpm, would make me suspect the battery or the non solid state regulator.  Flicker at any and all rpms.....go after elimination of everything one at a time until you get to the bad ground that will never be found and give up and go have a beer.

[sugarmcguinn@msn.com]

**UPDATE**

OK, so Honduran first said "I've seen that in headlights with broker filaments", and a few other posted the same, and someone posted "try a new headlight"

After Hondamans synopsis, I did test the old headlight, connecting it directly to the battery for about a half hour (giving it time to heat up fully) and then shake the crap out of it to see it anything was moving inside.  Then with a multi meter, .3 ohms resistance on high and low.  With that, I assumed the headlight was good.

But in all fairness, I hadn't tried a new "different" headlight.  This weekend, whilst trying to follow green ground wires from the bucket, under the tank, and down into the bowels of the frame, I thought to myself...  I'm going to all this work...  maybe I should just walk over to O'really's and grab a headlight and test it out.

Popped the new headlight in and COULD NOT get it to flicker once...  I even took a 30 mile test ride this afternoon and no flicker.

A few things of note, though...

 1. While messing around I tested the rectifier diodes (3 yellow wires. 1 Red. 1 Black).  It tested good (according to what I've seen on Youtube), but, while testing the new headlight I forgot to plug the rectifier  back in (about 20 min. of run time). Once I noticed the mistake  I quickly plugged it back in.  The bike runs with no noticeable difference that I can tell...  but it happened, so I thought I'd through it in.

2. I did pull apart both the right and left switch housings and douche them with Deoxit.  They sat overnight.

I don't know if one of these things contributed to the flickering issue, or if it was a bad headlight...

I did put the old headlight back on and couldn't get it to flicker either...  So who knows... 

The rub for me is NOT identifying for sure what the cause was...