Honda CBF125 losing electrics when at low revs

[Savage3000]

Hi, my Honda CBF125 is having an issue when I’m at low revs with the power that seems to be going to the electrics.

Firstly, I have tested voltage of the battery and it’s getting 13.5ish volts, and 14.something when I pull the throttle. I have also put my trickle charger onto the battery and it immediately says fully charged so I’m sure it’s not a battery issue.

I first noticed it last week now that the mornings have got darker, I notice the lights around the speedometer etc were going very dim when I pulled up to junctions or sat behind traffic etc. I then noticed that when I use my indicators, the rest of the lights seem to flicker dim and bright with the indicators, as if it doesn’t like sharing the power across an additional electric item.

I was also riding with my full beam, and when I pulled up to a junction, the bike cut out entirely, as if the full beam was draining all the power.

The bike idles in neutral fine (although with dim lights) and starts first time. I can also maintain brighter lights if I pull the clutch and stick a few more revs in whilst going slow.

Any ideas?

[stinkwheel]

What's the resting battery voltage like (everything off, been sat overnight).
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[xX-Alex-Xx]

Just because your battery is putting out the volts, doesn't mean it's putting out the amps needed. You need to properly load test the battery.
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DILLIGAF

[WD Forte]

As Alex says, voltage is only half the story
a bad contact may be at 13.5V or more volts but only allow a small amount of current to pass.

I forget how many times I've gone through checking and cleaning
a bikes/scoots electrical contacts and grounding to have all the odd problems go away.
____________________
bikers smell of wee

[stinkwheel]

A good example was my bike the other week after a reg/rec failure. It was reading 12V at the battery with everything off. It was down to 4.5 once the ignition coil energised.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Savage3000]

[stinkwheel]

Hang on. Doesn't a CBF125 have direct lighting?

Do the main headlights work without the engine running?

If not, what you describe is pretty much normal. With the exception of it cutting out.If you've fitted higher wattage bulbs, it will struggle even more to light them at low revs.

As far as I can find out from google (and I can't find a decent sized wiring diagram), it works like my wifes Honda Wave in which case the headlight is powered directly from the alternator only when the engine is running. If the rev speed drops, you get less power and the light dims.

Assuming it's like the Honda Wave, it uses halfwave rectified AC to power the headlight and the other half of the wave to charge the battery.

What we did with the Wave was fit LED headlamp bulbs. It's important to use a good quality, non-polarity sensitive bulb because the part of the waveform it uses for the direct lighting is effectively positive earth. Also important to note you can't use an LED stop and tail light.

For reference, these are the exact bulbs I fitted which work well. Google says the CBF125 uses the same fitment. They give a very slight flicker if the engine is near stalling point but are otherwise bright and powerful.
https://www.classiccarleds.co.uk/products/compact-led-headlight-h4-p43t-472-motorcycle-hi-lo-beam-conversion-9-32v
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jaffa90]

Found this,
https://bikesandtravels.com/biker.aspx?ride=953

[Nobby the Bastard]

[jaffa90]

[Savage3000]

[MCN]

A battery that shows fully charged is no indication that a battery is good.

The only sure fire method to determine if a battery is good or bad is to measure voltage across the terminals when a high load is being applied.
High Rate Discharge test.
A proper battery tester does that.

A new battery will cost you about <£40 for your bike.
https://www.tayna.co.uk/motorcycle-batteries/f/honda/ca125-95-96/
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[stinkwheel]

[WD Forte]

" it could be the Osram Nightbreaker 12V 60/55W headlight I fitted at the beginning of the year,"

Oh NOW you tell us!

Another owner 'improvement'

I'm currently getting a YBR ready for MOT with a melted headlight
that someone 'improved' with a 55/65 halogen in place of
the stock 35/35.

leds are an option and issa fack you get more bang for your buck with leds
BUT
A lot of H4 leds have a big assed heat sink sticking out the back and in the YBRs case it would have to be stuffed in an already packed rats nest.
As it's an always on type headlight, I'll have to do some tests to see if the heat sink temp will rise enough to be a problem.
Also, packing it in the closed back of a headlight doesn't really allow for good dissipation even if it didn't already have a shit ton of cables and connectors in there.
____________________
bikers smell of wee

[xX-Alex-Xx]

[Savage3000]

[MCN]

The bike should be well able to drive a 55w lamp.
The alternator will handle it.
But if the charging system battery is goosed then you will get problems.
____________________
Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[stinkwheel]

[Robby]

They are AC direct lighting to the headlight.

I once fitted heated grips to one. I thought I would do it the sensible way, direct feed from the battery triggered off a relay from the headlight circuit.

Started it up, and the relay was buzzing at 50hz. So I just wired the grips into the headlight circuit. They worked, but the LED indicator didn't.

This was on a bike that only got used around London, so headlights were just to be seen.

[stinkwheel]

[Savage3000]

[Robby]

I grew up in the sticks, I'm familiar with your pain.

The high wattage headlamp doesn't fix the problem. To be honest, nothing much does on bikes with direct lighting, apart from learning to use a lower gear and keep the revs up in corners.

It's a ballache, but you just need to ride slower and more carefully at night to keep within the limits of your headlight.

[stinkwheel]

[WD Forte]

AC lights?
You sure?
t'internet says it was made from 2009 on I would have expected better than that old 1970s type lighting.
I haven't seen a wiring diagram but the parts fiche shows a modern looking stator, with finned regulator and PGM-FI
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bikers smell of wee

[jaffa90]