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1975 Honda CB125S

8970 Views 70 Replies 10 Participants Last post by  knappyfeet
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I purchased this old 125 on offer up for $500. It needs a lot of stuff but it runs, rides great, and best of all it has a title and is currently registered… kind of a rarity for a $500 project on offer up or craigslist. My wife has been wanting to learn to ride on the street for some time .....she knows how to ride dirt bikes and stuff from years of desert trips...... but I figured it would be best to start off on something as small as I could find. As you can see it needs a few things and from just a preliminary inspection I would guess an additional $500 to $700 worth of parts……. So it could potentially be a $1200 motorcycle/project before I even take one rag to wipe the dirt off...but I feel it's worth it.

In my opinion there are 3 pressing issues that need to be addressed before she rides it and one is the front brake. It works but the inner workings are seized and just a big clump of rust. I thought it was a run of the mill front brake but it's some kind of cable squeeze contraption… something I've never seen before. It will stop now but it needs to be addressed. The 2nd thing is the carburetor. The engine sounds tight and not loose but the carburetor is not adjusted correctly or is not the correct one. It'll start…. Sometimes hard… It will idle high and then sometimes normal. It looks like at 1 point they replaced it with a Chinese knock off. I've had hit-or-miss issues with Chinese knock off carburetors so it may be that. It has 6800 miles on the clock and from the tapit covers it looks like the valves were probably never adjusted.

The 3rd thing is electrical. The horn and the headlight works and the tail light is dim. The previous owner told me it had a slow power drain so it may or may not be charging. I haven't taken a multimeter to anything yet so who knows but I'm preparing for the worst.

Good news is parts seem fairly abundant. Some things are dirt cheap and other things are through the roof. I can find a full electrical knock off wiring harness for 40 bucks new and mirrors and gators and little rubber things cheap.

So for now I will address the front brake before anything else so my wife can ride around in circles in a parking lot.. She's small at 5'2" and this bike is extremely small but something tells me she will outgrow it very quick.


It's nice to have a small bike back in the garage…. even if it is a work in progress. I'm sure things will surprise me along the way.

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The same disc and caliper were used on the Honda 78-78 MT-125R production road race bikes. Some guys replaced the calipers with hydraulic ones. Not sure with what. Probably Honda single piston from a CB 350, 400, 550, or 750
I have the exact same bike. Same year. Same color. Bought it to get around Mid Ohio Vintage Days this past summer.
As jaguar said, the cable front disc brake isn’t bad. You and your wife might find it to be ok. Especially since she is a new rider and may be more confident learning to use a front brake that would require more effort to lock the wheel than a retro-fitted hydraulic one may.
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When I got my bike, it had not run in years. It had under 900 miles on it. Inexplicably, the prior owner removed (and probably lost or damaged) the jet needle. He replaced it with a piece of solid copper wire. That wire didn’t stay put and ended up getting Inhaled into the combustion chamber—where it didn’t digest. Bent both valves, beat up the cylinder head and smashed the piston hard enough to collapse the top ring groove.

The carb was crusty and needed gaskets and a jet needle. I saw a complete carb on Amazon for $12.00 and change, shipped to my door. When it arrived, it looked great. However, when I installed it, the bike simply would not run. I robbed the bowl gasket and jet needle from it, threw the OEM carb in the HF ultrasonic cleaner and I was good to go. When and if I get a chance, I will see if I can blow compressed air through the idle circuit.

I would encourage you to see if the PO still has the original carb laying around, so that you can do the same.
Maybe somebody on this forum will have a carb laying around and will send it to you. I looked through my stuff, but don’t. 20 years and a few moves ago, had several. I will ask around and let you know if I come up with something.
Do you live near a M/C salvage yard? I am pretty sure that the carb from a CB/CL/SL/XL 100 is the same.
Be careful when buying side covers. The ones used on 1976(?) or 1977(?) and later 100s and 125s are different than those used in 1975 and earlier.
You can find the shop manual online. Check out DTT.
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Do you live in or near a city that has an old(er) Honda dealership? An old timer there may have something laying under his bench or at home.
Talk to the service manager. He will know which of his mechanics hoard parts. He will also know customers that do so and will know what is laying around in the parts department.
If you can get an OEM carb body, you can probably use many of the parts from the one that you have to make a functional carburetor. As mentioned above, I will ask around.
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