Topic: Headlight fades at stoplights?

[DammitDan]

I've noticed lately the headlight on my '82 650 fading a bit when idling at stoplights at night.  Jump the revs and all the electrics brighten up a bit.  The battery is fairly new, and I keep it maintained.  It occasionally has a slow start with the starter, but it usually kicks it right up.

Could this be a problem with only my battery, or something else?  I'm pretty sure the light isn't supposed to dim noticably when I come to an idle.

[78_SaltLick]

Possibly a bad cell in the battery? My bike died at a stoplight last weekend, i pushed it over to an alternator shop and we hooked up a charger to the battery, it was dead and couldnt hold a charge. Right before this, my bike did the same thing (light would go dim at an idle, and go brighter when i reved it). I was TOLD the battery in it was new by the guy i bought it from. We put a new battery in it, then started the bike and hooked it up to his voltage meter to see if my charging system worked (got the RPM's up and saw that it was charging the battery). Ever since then i havent had an issue with the lights going dim. The dude at the shop said it was a bad cell (one of the cells was completely void of water). Sounds like your charging system is working cause when you rev the engine the headlight gets brighter, maybe you just either need to fully charge your battery or get a new one. This is coming from someone who dont know much about bikes, but im trying to learn.

[SteveD CB500F]

I had this problem with a brand new battery in my son's Ford Fiesta.  It took several visits back to the shop to convince them that it was knackered.  "It's your charger / wiring / starter (?) / regulator etc" - anything but admit they'd sold me a dud.

[bistromath]

It will dim a bit even if mostly charged, but if it's that noticeable the battery is probably not healthy. Check the acid levels and invest five bucks in a hydrometer to check the specific gravity of the acid.

[eldar]

A lot of old bikes and even cars have this issue. Look at it like this. You battery at full charge is about 12.6 volts or so, when reved over 2000 the voltage is around 13.4 or so. Almost an extra volt, your headlight will get brighter. I had this on a couple older bikes. My 750 has always done this with any battery that was fully charged. You should not have a huge difference though. My turn signals will also blink a bit faster with higher rpm.
I have a friend with an Internation scout 2 that is a 1976 and his lights work the same way.

[DammitDan]

Well, it's not as though the headlight goes out or anything... It just dims at an idle.  Maybe the closest comparison would be between a domestic 40w lightbulb and a 100w lightbulb?

[eldar]

Yeah it just drops a little. Not a lot, does not go out or anything like that.

[pmpski_1]

I'm having this problem as well.

I just rode the bike after a few weeks. I did not have the battery charger on the bike during this idle time. When I got on I hit the starter button and it slowly cranked, like the battery was going. I kicked it a couple of times and it fired up. I warmed it up, killed it, and hit the starter again to see if it was charging. No problemo, fired right up.

Once I got on the road I noticed that the blinkers would only work if it was rev'd above 3k or so. I didn't ride too far, but the blinkers never worked below that 3k.

My battery is new and I have a new flasher relay that worked the last time I rode. I guess the battery had a bit more juice last time. I'll check to make sure that the battery is topped off. Any other ideas if that doesn't solve the problem? I like having all of my signals working.

[Mark M]

It never hurts to give old connectors a good clean from time to time.

[dpen]

Check all your electrical connections first.
Then invest in a multimeter & check your charging according to the manual.
A slight dimming of the lights at idle is normal as, at idle, the alternator is not charging & you're running off the battery.
Check the FAQ for details by people more knowledgeable than me with electrics.

[eldar]

New turn relays are different than what we originally had. They require more wattage to use whick is fine for newer cars and such as their charging systems are always charging. They have too since there is such a large drain on the electrical system. Our bikes do not do that of course so flash will act differently below certain rpm. Mine does not flash too brite or fast until I hit 2000 rpm. I however do not have an issue with my starter turning slowly.

[pmpski_1]

Interesting Eldar.

I think the battery was on full charge when I replaced the relay, so it may have worked a bit better at that point. The slow starter isn't a problem so much, but I'm interested in the battery drain over 2 weeks.

Winter project, here I come!

[eldar]

I guess I dont think that these charging systems keep our batteries at full charge ever except when running high rpm. So any time you idle like before you put away the bike, the battery is discharging from ignition. Something like that anyways.

[Mainer4]

The 650 has one of the "weaker" charging systems out there for the SOHC4 (I have the other one, a 400F).  But even with my '76 750 the turn signals will slow down while idling and yep, my headlight dims slightly also.  Not to worry, just another artifact of owning a SOHC4!   

[Gordon]

Not to worry, just another artifact of owning a SOHC4!   

I always liked the little quirks that older vehicles have.  I used to own a 1974 VW van, and at night with the lights on, not only would the headlights dim in unison with the blinkers flashing, but the engine idle speed would fluctuate up and down right along with them. 

[BobbyR]

I would check my voltages, and adjust the regulator. As far as connection, I solder them.

[pmpski_1]

I don't mind the lights dimming a bit or the blinkers flashing a little slower. I do mind that they don't flash while sitting at a stop light getting ready to make a left turn. I may try an LED conversion for my blinkers. I've heard that the brake lights aren't as bright if you use LEDs, so I'll do the blinkers first. It'll be slick if I can re-use the stock shells ... or I could go for a clean look and get some aftermarkets.