CB125K3 Rebuild

Craizeehair

Craizeehair

Member
Joined
Dec 31, 2023
Total Posts
23
Total likes
18
Location
UK
Hi all,

I took ownership of a French origin CB125K3 in the summer of 2025, the bike was initially said to come with paperwork but unfortunately it turned out to be an old log book for a different frame. I have since been trying to get the bike registered here in the UK, it’s been a bit of a drawn out process but I have now got the bike registered and paperwork sorted. I’m now in the process of piecing the bike back together and seeing what I have and what I need. I have had the bike running, I was able to wire enough to start the bike, so I know it’s a runner.

I would like to check compression and see what I have, there is no electric start on this bike, so before I get things wrong from the get go, could anyone advise on the best / correct way to check compression to give me the correct readings for this model. I believe testing with a warm engine is best, is this correct?

Many thanks in advance.
 
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ancientdad said:
And one we didn't get here in the US. Kind of like a mini 175.
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Almost exactly the same as a 175 apart from the engine, frame and running gear appear identical to a CB175 K4 or K5. Even got the hole in the frame for the CD175 single carb air filter. Wonder what the redline on the tacho is, 10.5K like the 175, or higher ?
 
Richard Pitman said:
Almost exactly the same as a 175 apart from the engine, frame and running gear appear identical to a CB175 K4 or K5. Even got the hole in the frame for the CD175 single carb air filter. Wonder what the redline on the tacho is, 10.5K like the 175, or higher ?
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Just found this source, not convinced of the accuracy as it seems this model isn't as popular with the usual, reasonably reliable sites like motorcyclespecs.co.za. Picture at this site is correct, specs could be I suppose. If true it shows 15 hp at 11,000 rpm

Honda CB125K3

UK motorbike web directory and search engine, one of the fastest growing motorctcle websites in the UK
www.motorbike-search-engine.co.uk
 
I’m currently going through the wiring harness, there’s has been some chopping about but not too bad. Everything looks like it can be repaired properly.

I have one wire that I’m not too sure of, it’s a brown with blue tracer, am I correct in thinking this is the indicator buzzer, so wouldn’t be used / relevant to this French origin bike? If that’s not correct, would anyone know what it is, I can’t see it on any of the wiring diagrams that I can find.
 
Is the brown blue stripe wire an additional one added into the harness when you say some chopping has been done on the harness by a PO?

Here is a Canadian wiring colour diagram that can be used as a guide for some ideas. The brown/blue stripe isn't shown as a combination on here. The brown wire in general is associated with running lights, dash lighting and around taillight areas too. It also supplied a headlight bucket location for a solid brown wire with a female connector. It was an off the key switch controlled 12V+ unused connection point for accessories.
Where is the wire presently found on the harness? Are there other identical coloured wires elsewhere in the harness? If so where are they located?



Honda Wire Color Codes (rev. 2022).jpg
 
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The brown blue wire is original to the switch as far as I can see? I did read that it was the indicator buzzer but i presume not as it’s from the switch on the side of the headlight?
 
Craizeehair said:
The brown blue wire is original to the switch as far as I can see? I did read that it was the indicator buzzer but i presume not as it’s from the switch on the side of the headlight?
Click to expand...
It's difficult for those in the US to help because we didn't get that model here, so we don't have any documentation for it like a wiring diagram for the appropriate country.
 
A closer look at the bike and handlebar switches shows me it has a Euro style headlight on-off switch, and I see it dangling from the harness on the left side of the forks. Since the right handlebar switch only has a low and high beam switch, maybe that wire connects to the headlight switch.

1769026400568.png
 
Craizeehair said:
The brown blue wire is original to the switch as far as I can see? I did read that it was the indicator buzzer but i presume not as it’s from the switch on the side of the headlight?
[/QUOTE

I’m not sure what’s happened to this post, I’m new to this, so apologies!
Thanks for the suggestions, I will keep searching and see what I can find regarding the wiring.
Click to expand...
I’m not sure what’s happened to this post, I’m new to this, so apologies!

Thanks for the suggestions, I will keep searching and see what I can find regarding the wiring.
 
I did but I think I clicked on quotes and then couldn’t figure out how to delete that? This is the only site in use without tapatalk, I will figure it out quickly I’m sure.
 
Craizeehair said:
I did but I think I clicked on quotes and then couldn’t figure out how to delete that? This is the only site in use without tapatalk, I will figure it out quickly I’m sure.
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When you quote a post, as I'm doing with yours, you can delete parts of the quote as well as divide the quote to respond to parts of it separately. The key with a single quote is to be sure you are out of the quoted area when you type your own words. You simply go to the bottom of the quote and click below the grayed area, then type.

Here's an example of dividing up a quote - you just put your cursor where you want to divide the quote and then hit "Return" on your keyboard (L shaped arrow probably)

Craizeehair said:
I’m not sure what’s happened to this post,
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Me either
Craizeehair said:
I’m new to this, so apologies!
Click to expand...
No apologies necessary
Craizeehair said:
Thanks for the suggestions,
Click to expand...
No problem
Craizeehair said:
I will keep searching and see what I can find regarding the wiring.
Click to expand...
Great!
 
Looks like Tom is correct. Here's a photo of the UK spec CB175 lighting switch, mounted in the headlamp shell, complete with brown wire with blue stripe.

Trying to decode the colours without taking my own bike apart. Yellow and White wires are the charging circuit wires that connect when the head lamp is on. Black wire is ignition switch controlled live feed, so I'm guessing the mystery brown/blue wire is the switched live feed to the handlebar dip / main switch, and the brown/white wire is the side lights feed.

1769095931874.png
 
Thanks for all the help, turns out it wasn’t a huge mystery after all. The brown / blue isn’t shown on any wiring diagrams I could find and I was trying to figure out what was what with the wiring on the controls that came with the bike, these as it turns out were not factory wiring. I have some NOS controls tucked away and when I checked those there is a brown / blue wire from those, so all sorted now, it is s a feed to the handlebar switch.
 
I recall seeing a brown/blue wire in my harness. Not sure if it's on the main or one of the switches.

My wiring is created by several model bikes.

So electrical issues out of this world for me.
 
I managed to get the wiring harness sorted and fitted all the electrical components in place. Everything was wired up, connected and tested. I need to replace the flasher relay and the horn, everything else checked out ok, so I was quite happy with that.

I don’t have a front brake cable to test the front brake switch but I do have one on order, so I should have that by next weekend but I don’t envisage any issues there. The wiring diagram in the FSM doesn’t show a front brake switch but my understanding is that it forms part of the front brake cable?

Considering a lot of this bike was in boxes, I believe that I have been very lucky, the vast majority of parts are here and this bike should be pretty straightforward to piece together.
 
Would anybody have any information or diagrams of correct routing of the (throttle, clutch etc) cables ?

The previous motorcycle that I revived was a CB360 and the FSM had really good diagrams showing correct routing of cables and wiring but I can’t find anything for this CB125K3?
 
Craizeehair said:
The wiring diagram in the FSM doesn’t show a front brake switch but my understanding is that it forms part of the front brake cable?
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That's how it was sold back then, but those cables are next to impossible to find these days and really didn't turn the brake light on as soon as it needs to be, so you had to use the rear brake in conjunction with the front (not that you shouldn't do it already) in order to be sure you had a brake light. Pretty strong lever pressure to get the switch to complete the circuit. Your alternative is to buy a newer front brake lever perch with the pre-drilled hole for the later micro-switch Honda used, and the wire colors to connect it to should be the same in your headlight case.

Correct perch from 4into1 (called chrome but likely polished)

4into1.com

Honda Brake Lever Perch - 53171-312-003 - Chrome

Reproduction Honda chrome brake lever perch. This brake lever perch is found on lots of 70's Honda dirt bikes and can be used on just about any front drum brake bike you want.
4into1.com 4into1.com

Or satin black

4into1.com

Honda Brake Lever Perch - 53171-312-003 - Black

Reproduction Honda black brake lever perch. This brake lever perch is found on lots of 70's Honda dirt bikes and can be used on just about any front drum brake bike you want.
4into1.com 4into1.com

Here's an OEM Honda switch

Amazon.com: HONDA 35340-329-010 SWITCH, FR. STOP : Automotive

Buy HONDA 35340-329-010 SWITCH, FR. STOP: Engine - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com

and amazingly, a lower priced aftermarket one from those guys in Houston

https://www.those guys in Houston.com/honda-front-drum-brake-light-switch-cb175-cb200
 
Craizeehair said:
Would anybody have any information or diagrams of correct routing of the (throttle, clutch etc) cables ?
Click to expand...
That bike was not sold here in the US so the VHT Library doesn't have anything helpful, but someone in Europe or Canada? where it was sold might have pictures. If not, pics from the internet are likely as good as you'll get.
 
Craizeehair said:
Thank you, I will see what I can find.
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The cables on most Hondas back then, possibly prior to the half-circle loop that bolted to the forward pair of handlebar clamp bolts for containing the cables, were routed across to the other side of the frame from their point of origin, similar to this annotated screenshot below (except under the bars and top bridge, of course).

1769435702667.png

The clutch cable would route similarly but across to the right side of the frame, then under the main backbone it would cross over to the left and into the front sprocket cover where the clutch lifter mechanism is located. Generally the throttle cable was routed above the left side forward tank mount rubber and post, the clutch cable sometimes above the tank rubber/post on the right side but sometimes below it depending on the length of the cable and available slack. Handlebar switch wiring goes straight down into the headlight case and the main harness.

Aside from the different headlight arrangement and location of the factory cable loop on the forward handlebar mount bolts, this is a picture of my 450's cable routing. The front brake cable would typically go through the loop as well, but my forks are raised in the clamps to lower the bike and as such the front brake cable can't go through it due to length and increased cable binding. You want the routing to provide the most relaxed bends in the cables as possible for free movement.

20240402_154542.jpg
 
ancientdad said:
The cables on most Hondas back then, possibly prior to the half-circle loop that bolted to the forward pair of handlebar clamp bolts for containing the cables, were routed across to the other side of the frame from their point of origin, similar to this annotated screenshot below (except under the bars and top bridge, of course).

View attachment 54561

The clutch cable would route similarly but across to the right side of the frame, then under the main backbone it would cross over to the left and into the front sprocket cover where the clutch lifter mechanism is located. Generally the throttle cable was routed above the left side forward tank mount rubber and post, the clutch cable sometimes above the tank rubber/post on the right side but sometimes below it depending on the length of the cable and available slack. Handlebar switch wiring goes straight down into the headlight case and the main harness.

Aside from the different headlight arrangement and location of the factory cable loop on the forward handlebar mount bolts, this is a picture of my 450's cable routing. The front brake cable would typically go through the loop as well, but my forks are raised in the clamps to lower the bike and as such the front brake cable can't go through it due to length and increased cable binding. You want the routing to provide the most relaxed bends in the cables as possible for free movement.

View attachment 54562
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That speedo, that's the kind I need.
I bought one from a guy that said it would work, but when I got it the thing was a mess.

Others I found are being priced at a "get rich quick" prices. Oh well, is a nice looking speedo.
 
oldhondas said:
That speedo, that's the kind I need.
I bought one from a guy that said it would work, but when I got it the thing was a mess.
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Ah, but I have a spare if you're interested. I chose to use the nicer one of the two I bought, but the other one isn't bad at all.
oldhondas said:
Others I found are being priced at a "get rich quick" prices. Oh well, is a nice looking speedo.
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I hear you, the CB77 stuff goes like the CB450K0 stuff. Thanks, I'll PM you some pics so we get this thread back on the rails.
 
A bit late to this thread, but if still useful, I can help with wire diagrams, partslists and some manuals/ documentation for this models ( cb125 k2 -k5 ) i have 2 of the french models myself. Pm me if you would want anything.
 
HondaJR said:
A bit late to this thread, but if still useful, I can help with wire diagrams, partslists and some manuals/ documentation for this models ( cb125 k2 -k5 ) i have 2 of the french models myself. Pm me if you would want anything.
Click to expand...
Thank you, I will be in touch I’m sure!
 
I am looking to fit the battery tray and have located the battery cushion rubbers on amongst the bits and bobs.
Looking at the parts diagram it appears as though the rubbers sit on top of the battery tray, is this correct?

My instinct tells me that they sit below the flats of the battery tray against the frame, if they aren’t fitted below, then the battery tray sits directly on top of the frame with a gap between the two, can anyone confirm?

IMG_1625.jpeg

IMG_1628.jpegIMG_1627.jpegIMG_1629.jpeg
 
Yes, they sit between the frame rail and the battery box, as in your last two pics.

Here's my CB175 for comparison.

1770913439882.jpeg

I added extra rubber washers under the top plain washer, parts 28 and 32 in this diagram.
1770913921722.png
 
Last edited:
Craizeehair said:
Hi all,

I took ownership of a French origin CB125K3 in the summer of 2025, the bike was initially said to come with paperwork but unfortunately it turned out to be an old log book for a different frame. I have since been trying to get the bike registered here in the UK, it’s been a bit of a drawn out process but I have now got the bike registered and paperwork sorted. I’m now in the process of piecing the bike back together and seeing what I have and what I need. I have had the bike running, I was able to wire enough to start the bike, so I know it’s a runner.

I would like to check compression and see what I have, there is no electric start on this bike, so before I get things wrong from the get go, could anyone advise on the best / correct way to check compression to give me the correct readings for this model. I believe testing with a warm engine is best, is this correct?

Many thanks in advance.
Click to expand...
Hello Caraizeehair,

a little bit late, sorry, I have missed the thread.

For compression check in this biek it would be best to have:
1) shortest tube with pressure gauge to reduce volume. Cylinder capacity is really small, so pressure readings can be mismatched with long tubes.
2) You can use wheel or cord/cordless unit to turn the engine to obtain proper pressure.

I have got FSM for older model (K5) so I can support You in doubt, as in most cases construction is almost similar.

P.S. nice bike :)
 
AndrewJK said:
Hello Caraizeehair,

a little bit late, sorry, I have missed the thread.

For compression check in this biek it would be best to have:
1) shortest tube with pressure gauge to reduce volume. Cylinder capacity is really small, so pressure readings can be mismatched with long tubes.
2) You can use wheel or cord/cordless unit to turn the engine to obtain proper pressure.

I have got FSM for older model (K5) so I can support You in doubt, as in most cases construction is almost similar.

P.S. nice bike :)
Click to expand...

In my bike, there is only Brown/White wire for illumination for tacho.
 
Progress has been a bit slow as I have been trying to find a clutch and front brake cable the correct length, I have bought a couple but they are too long, so I have had a go at shortening them myself. I bought myself a cheap solder pot and the correct sized replacement nipples and had a go, they came out pretty good and should now be ok.
IMG_2344.jpeg
 
The cables are fitted and everything works fine, I had it riding up the road, it goes through all the gears and stops!
IMG_2536.jpeg
IMG_2535.jpeg
I did notice that there was oil leaking from around the tacho cable when it’s hot, I presume that’s a straightforward fix?
IMG_2534.jpeg

I’m not sure what I will be doing with the bike now, I have a CB350K2 frame currently at the powder coaters after having some welding done, this will need to be reassembled soon, that was my main project before I found the welding needed doing, this little 125 was bought to give me something to do whilst waiting for that.

Thanks for the help and guidance all.
 
Hello Craizeehair,

I had leak in the same spot. The seal was avalaible at the Honda dealership. The size is quite unusual.

gemini.jpg
gemini_2.jpggemini_3.jpg
 
Craizeehair said:
The cables are fitted and everything works fine, I had it riding up the road, it goes through all the gears and stops!

I did notice that there was oil leaking from around the tacho cable when it’s hot, I presume that’s a straightforward fix?

I’m not sure what I will be doing with the bike now, I have a CB350K2 frame currently at the powder coaters after having some welding done, this will need to be reassembled soon, that was my main project before I found the welding needed doing, this little 125 was bought to give me something to do whilst waiting for that.

Thanks for the help and guidance all.
Click to expand...
Glad you got things sorted. Your front brake cable is adjusted quite a bit at the wheel, which tells me the shoes are pretty worn.
 
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