[Flaekingr]

Hey folks.

I've come across an issue that actually made me decide to lay up the bike over winter, which I never do.
Last October I took my 04 500 KS on a holiday from northern England down to the south, across to London and back home. Bike was amazing through the whole trip, I made sure to go over the potential problem areas contstantly and all was well. Except on the way back north, about 150 miles from home at about 9pm. My tail light had blown and I didn't feel like getting taken out by a semi, so I stopped into a services to see what could be done. The shop didn't stock the right light, and I had a box of 10 of them...that I'd left at home
So I used a bit of folded cardboard to jam the brake light switch open, figuring I'd rather have a solidly on brake light than no light at all. It worked, but the bike only ran for about 20 seconds before dying, then 10, then 5, then it wouldn't start at all. I figured it was draining the battery too much at idle, so I removed the bodge and it started no problem, but I obviously still couldn't ride it and expect to arrive home unscathed. A biker eventually rolled in who happened to have a spare, (big shoutout to biker camaraderie!) and I got ready to leave. Same thing though, the bike ran for about 20 seconds, then less, then not at all. I eventually had to call my breakdown company and arrange a pickup, which was a whole other nightmare that I won't bore you with. About an hour later I tried the bike again, lo and behold it started and stayed at idle, so I jumped and rode home while I could. It's worth noting that the tail light filament had gone again by the time I got home, but not the brake light filament.

So about a week later I replaced the bulb again and went for a ride. I got maybe 10 miles up the road, and the bike just cut out on me. I was cruising at about 40mph, I think I'd just rolled off the throttle to stop for an intersection, or was just about to, and yeah, engine just cut out. I pushed the bike to a safe spot and tried to kick it over, nothing. I decided to give it half an hour and try again, a nice person stopped to check on me (shoutout again to biker camaraderie) and we had a wee chat about old bikes. So the bike started again right away, I rode it home and it's been in the garage since. I don't have room in my tiny garage to actually work on it and it was getting to cold, wet and miserable to be outside trying to chase this issue down.

Congratulations if you've made it this far. I know I've banged on a bit but I wanted to paint a thorough picture of what's going on. So, what's going on? Where do I start? The weather is getting better and I'm real ancy to get out on two wheels again, but I don't fancy being stranded.

Any help and advice would be great!

[AzCal Retred]

Sounds a lot like a cooked battery, probably caused by the Reg/Rec. Incandescent bulb filaments open up due to excess current heating them up. Excess current is driven by excess voltage. Excess voltage "cooks" the battery. A lead battery often "recharges" a bit if left to sit under zero load. That's a chemical voodoo effect & consistent with what you saw.

IF your Reg/Rec on your (Kick Start?) 500 parks at 16-18V like two of mine do, that eats lead acid batteries. A cheap work around is to acquire an 18V NiMH tool battery and use it to replace the cooked lead acid battery. The 18V NiMH battery could care less that the Reg/Rec parks at 16-18V. I stole one out of an old cordless drill. The "new" 4-wire machines have an AC headlight, that's the big load. All the battery does is run the ignition coil, brake & tail lamp, very low load. It just needs enough "ongawa" to last long enough to kick start the machine. I wrapped up mine and put it in the LH toolbox.

Using a LED 1157 tail lamp "bulb" reduces the main drain to a few tenths of an amp. LED's usually have a wide operating voltage range (9V-25V), but that'll be on the package it comes in.

Do some voltage checking and see what's ACTUALLY going on. If it is the Reg/Rec overcharging and you want to stay stock, at least put a Boyer Reg/Rec (powerbox?) in there instead of the OEM Reg/Rec. They work very well, regulating at a relatively flat 13.8V-14.2V charging. A bit more but your new battery will thank you. Plus they have a "dead battery kick-start" feature built in.

Investigate & report back!

[stinkwheel]

As above, if it's popping bulbs and running badly, I bet the reg/rec has failed and is putting out excess voltage. It would certainly have cooked the battery, it may have cooked the alternator.

So, test output voltage across the battery with the engine running, should be in the rage of 15-ish volts.

Check the static resistance of the alternator windings. The wires going from the alternator to the rectifier. You should get a low coil resistance between the two wires in the ohms range (not kiloohm range, not less than a couple of ohms). Check resistance between each wire and earth, should be an open circuit.

You can fit pretty much any reg/rec to these bikes, they all do pretty much the same thing. Mine has a ZX6R one. I did a how-to and it should be appropriate for your bike.
https://www.instructables.com/Fit-a-Japanese-Regulator-Rectifier-unit-to-a-12v-A/

[Flaekingr]

Thanks for the replies and advice. I guess I should've mentioned that I do in fact have a boyer powerbox installed, and it's only about 6 months old. But yeah, not impossible for it to fail I suppose?

[AzCal Retred]

If the Powerbox is working, the charging voltage to the battery with the engine spinning ar fast idle will be in the range of 13.8V - 14.5V. Battery cooking starts at a sustained 15V or more. Your VOM will tell the tale - get some numbers.

Batteries fail internally in many ways. There is no guarantee of lifespan. Charge it on the bench, see if it holds a charge overnight (13.5 down to 13 - 12.9). There are battery load testers at the auto supply. Often a new battery has the same healing juju as a fresh spark plug...

[stinkwheel]

Also remember a reg/rec can't dump power if it has a bad earth.

[Lone Wolf]

Batteries fail internally in many ways. There is no guarantee of lifespan. Charge it on the bench, see if it holds a charge overnight (13.5 down to 13 - 12.9). There are battery load testers at the auto supply. Often a new battery has the same healing juju as a fresh spark plug...

Wotcha.

A battery can seem fine, voltage-wise . . . . but fail when any load is applied.
This caught me out on the way home once .

https://www.youtube.com/watch?v=InbWlPOWXjA

[stinkwheel]

Here's a very long and tedious video (which frankly, I uploaded for the sheer hell of it because I'd left the camera on accidentally) showing how a 350 bullet runs on a flat, nearly dead battery.
https://youtu.be/tcQjmfst7so?si=j3_xo-RShwKr1Pzo&t=735

[hortoncode3]

When I first bought my 500, an ‘05 Olive drab non runner in Portsmouth New Hampshire USA, it refused to start. Someone had messily cobbled up an antique looking STOP type light on the back and besides looking sketchy, was a total hack job too. Fortunately the now former owner (who I might add was NOT responsible for all of this mess)  had a large box of parts including the original ugly half brick tail light assembly. After I had taken the botched one off, and installed the origonal one, the bike popped right off and ran fine. I can only assume something in the wiring in the light was off and either it didnt ground properly and messed the system up or the light itself had a dead short somewhere.
My advice, check all grounds.
Further, last spring this bike crapped out about 100 yards from my house. I could kick it and it would idle, but immediately die when I twisted the throttle. Plus, the electrical would wink out too, speedo lights, headlights, everything. Wiggle the handlebars and it would all come back. Now mind you, I kick start this thing as the starter had been pop-corned years before I bought it.
I dragged it home and there it sat. Finally, I decided I had a partial break somewhere in the wiring supplying power to the coil and main circuit. It HAD to be from the battery to the fuses, I imagined. SO, in one of the most stupid things I have ever done with this bike, I prepared to start it. Kicked it over about 10 times with the key off, key then on and tried roll it over to TDC using the ammeter. Still ok. Then I kicked it, thinking it would start and I would wiggle that offending wire to see if it would die. WRONG. It wasn’t TDC and it kicked me back, tearing my Achilles in my left foot. So, I was out all summer. No riding. Long story short, after I recovered I hauled it out of the shed and chopped that wire out and replaced it with a heavier one. After considerable reflection, and caution, I decide discretion was the better part of valor and I rolled it down the hill and popped it into gear. Started right up. Rode it for 10 miles. Came home and shut it down. Then I kicked it. Still started perfectly. Runs great.
SO, check that power wire!

[Black fingernail]

Apart from the electrical problem, it won't hurt to check the rubber carburettor inlet tube, these split so regularly, I use car radiator hose, (I am currently trying silicone).
You may just have a bit of bad wiring to the bulb, and a split hose.