Honda CB 125 RS

[caferacer]

Hi everyone,

Bought myself an old CB 125 RS having recently passed my CBT. No mechanical knowledge of motorbikes and without a haynes manual for this bike, I'm having a go at 'winging it'.

I know there are a lot of people who are very knowledgeable on the various honda 125s so it makes sense for me to share my questions on here.

https://desmond.imageshack.us/Himg855/scaled.php?server=855&filename=3gedc1348.jpg&res=landing

https://desmond.imageshack.us/Himg856/scaled.php?server=856&filename=4gedc1355.jpg&res=landing

[TheSmiler]

Admire determination but can't see this ending well .. you could of got this amazing looking cg and been on the road.

https://www.ebay.co.uk/itm/290768737967?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
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CB125>CG125>GN125>ER5>K100RS>R1100RS>K100RS
A2 completed 23/07/15 Ready for the Golden Crisp Packet

[caferacer]

[Teflon-Mike]

[SnowTigeress]

[Teflon-Mike]

[SnowTigeress]

[caferacer]

Thanks for your responses SnowTigeress and Teflon-Mike!!! I have literally read both your threads the whole way through - sad I know but they really inspired me to have a go myself.

The bike is running nicely at the moment. Suspension is great, brakes working nicely after a bit of work and the electrics are pretty much there now.

Yeah, that budget has gone out the window - surprise! but I'm keeping it as low as I can because I know this is an old bike.

I've fitted some nice old clocks and a round headlamp and I'm looking for bullet indicators for it and a smaller tail light. Just not sure how well the lower seat would really work on such a small bike!

Considering painting the wheels.

At the moment the air filter box is off as I was considering fitting an after-market and making a new bracket for the battery. I really like having the gap in the bike there.
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HONDA CB750F; HONDA CB125RS

[Matt-]

[blurredman]

Yay for the 205!
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CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S, 1979 MZ TS150.
Current: 1973 MZ ES250/2 - 18k, 1979 Suzuki TS185ER - 10k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 (295cc) - 40k, 1989 MZ ETZ251 - 51k.

[janner_10]

That look likes 1 big bag of sh!t!!

Hear me out though, you will learn so much about your bike and bikes in general rebuilding that, doesn't really matter (within reason) what it costs to get it working again - sense of satisfaction will be enormous.

Best of luck with the project, keep the thread updated.
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Yamaha FZS600 (Now gone to heaven) > CBR600F4i (SOLD) > '99 YZF-R1

[caferacer]

[caferacer]

I wish I'd taken more photos of the bits I've done now, if anyone needs any help I'm probably the wrong person to ask but I'd be more than willing to try and help in any way I can.

As I think I mentioned above - another cost was the £10 I forked out for the original owners manual. I couldn't believe the lack of info on the web - owners of the RS are clearly tight as ! so I've got all the wiring diagrams and specs for the bike if anyone needs them - just ask and I'll upload.

[SnowTigeress]

[caferacer]

Haha, ashamed to admit they are 'Cougar' tyres... budget to say the least!

Here's about a million photos to make up for failure to update thread.

https://farm9.staticflickr.com/81175/8013160372_9116bb38db_z.jpg

https://farm9.staticflickr.com/83110/8013160438_c699810d7a_z.jpg

https://farm9.staticflickr.com/80132/8013157479_fe5c343688_z.jpg

https://farm9.staticflickr.com/83113/8013157615_471b8738cc_z.jpg

https://farm9.staticflickr.com/84153/8013157731_a2a00922f2_z.jpg

https://farm9.staticflickr.com/81029/8013160958_5335f3fa02_z.jpg

https://farm9.staticflickr.com/81443/8013161066_4e4949e558_z.jpg
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HONDA CB750F; HONDA CB125RS

[symonh2000]

Should be quite a nice bike when it is done.

I would put money on it being faster than most 4 stroke learners that you buy today as well.
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Four strokes is two strokes too many.

[caferacer]

[Pol Anorl]

[Teflon-Mike]

Honda - CB 125 RS
1983-1986
https://www.motorbikespecs.net/images/Honda/CB_125_RS_83-86/CB_125_RS_83-86_1.jpg
Brakes
Front: Disc
Rear: Drum
Dimensions
Length: 1,960 mm (77.2 in)
Width: 745 mm (29.3 in)
Height: 1,070 mm (42.1 in)
Wheelbase: 1,285 mm (50.6 in)
Dry Weight: 100 kg (220 lbs
Fuel Capacity: 11.0 litre
Electrics
Voltage 12v
Spark Plugs (Iridium) NGK DR8EIX
Engine
Type Air Cooled 4 Stroke SOHC Single
Bore x Stroke 56.5 x 49.5 mm (2.224 x 4.335 in)
Compression Ratio 9.2 : 1
Displacement 124 cm2 (7.53 cu in)
Lubrication System 0.8 litre
Transmission
Sprocket front 16
Sprocket rear 36
Chain Number of Links 108
Misc.
Motorcycle Style ROADSTER
Tyres
Front: 275-18 Tubed
Rear: 300-18 Tubed
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Bike was a revamp of the earlier CB125S & CB125J of the mid '70's, using the faithful little Overhead cam single, which had been deemed rather 'fragile' tuned to the extent it was in the early drum braked 125S, to deliver 12bhp. The 'Street-Scrabler' variant of the 125S, the SL was slightly de-tuned to 11bhp and provided the basis for the later, 'bullet-proof' as long as they got thier oil changed XL125 Dirt-Bike, from which Honda took the engine to motorvate the CB125RS.

Its related to the CG125, in as far as that was essentially the original 125S, fitted with retro-tech push-rod engine, delivering 10bhp, for 'developing' markets.

But the 125RS was a 'little gem'. More powerful throughout the rev range, and lugging 15-25Kg less mass than a CG (depending on variant), was a very much more 'spritely' little device with slightly more composed suspension.

The 125 Super-Dream only had slightly more power, but was lugging around 25Kg more mass to get it. It was the 'faster' bike, though point to point there would not be much between them on anything but a fast sweeping A-Road. Super-Dream with more sophisticated mono-shock suspension, more powerful twin piston front brake, and that howling 12,ooo rpm motor would be a little more 'composed' doing it.... while a CG would need a brave or stupid rider to try and keep them in sight, his engine lacking the 'urgency' hauling out of corners, and wheezing when stretched to higher speeds, and getting VERY bouncy through corners..... Only time a CG was likely to go past either the 125RS or 'Duper-Dream was on the way into a corner..... with smoke coming off the inefectual front drum brake.....

A 125 Super-Dream, in decent state is good for a genuine, 70+mph. I have had one up to 70 two-up, and 75, solo, on GPS snail-trails.

The 125RS is probably only a couple of points off for top speed. Its certainly a 70mph motorcycle.

The CG125, is really only 'good' for 65, and favorable conditions that would see it much beyond that, would also benefit a125Rs or 'Dream.

The genuine article Honda CG125, is probably slightly quicker than any of the (chinese) copies it has spawned, and they PROBABLY are in the majority of modern 4-stroke bikes on offer today.......

Which really only leaves a handful of Japanese or European four-strokes for it to square up to.

Yamaha YBR125? Pretty good comparison. Yamaha's answer to the CG125, with its overhead cam SR engine..... 11bhp, claimed 70mph top speed, and 125Kg......

Its actually 'faster' at least on paper than the Honda CBF, which with a claimed 12bhp only manages a claimed 65mph.

The Water-Cooled, four valve CBR125, boasts more power, and a little more speed. On paper the full A1 complient compliment of 14.5bhp, and 72mph...... but carrying as much mass as the old CB125 Super-Dream.

The CBR on paper is within a smidgin of the Yamah YZF-R125, and that powers the Riaju, Derbi & Aprillia four strokes I believe.

There ISN'T a HUGE difference between any of them for performance, and that 70mph top speed, is all VERY condition dependent.... condition of the bike, AND road conditions!

That little 125RS.... its got the 'potential' to cut it with the modern kiddie-go-kwik bikes......

The 'old' Super-Dream, certainly has, and point to point, applying 30 odd years of experience to the job, have left some 'young-turks' on plastic-fantastics shrinking in my mirrors down the lanes.....

On the public road.... the differences in rider skill or stupidity, will almost always be FAR greater than the differences in bikes capability. A complete nutter on a 250 Super-Dream can go faster than Mr Cautiouse on a Hyabusa, for as long as he don't come off!

But between the four-stroke 125's, the capabilities are SO close you don't need to have THAT big a disparity in rider ability or prudence!

That little 125RS? specs are enough to put it at the table for sure. It may not have the bigger power number, but it does have a relatively big advantage in that VERY low weight.

But missing the point, this bike was ALWAYS about cheap thrills.....

Super-Dream was built to match the two-stroke sports bikes on performance and beat them on sophistication.

CG125 was built to match the two-stroke commuters for low cost, total utilitarian transport.

CB125RS was built to deliver a compromise between the two.

Nearly thirty years on? It's a pretty good place to start a project. That twin-shock rear suspension is simple and durable and easy to overhaul. The single piston brake, likewise useful. Forks conventional. Motor, rugged, and easy to work on.

And CafeRacer is starting in the right place tackling the bits that matter most, making sure it will stop, steer and handle.

If the motor hasn't got gummed rings or need a rebore, or a flat cam, or hammered tappets.... little fettling ought to see it find its old sparkle well enough, and the ingredients are all there, for it to have the potential to do its job, and offer a LOT of fun for not a lot of dosh.

Certainly more fun thrashing an old bike you have built, to within an inch of its life, thinking "Whey-Hey! I made it do this!.... I hope it doesn't blow up! What the HECK.... I can rebuild it if it does!" and taking another handful of throttle stretching the cable a bit more tryng to find some extra go.....

Than..... sitting on a plastic fantastic, going into a corner a bit hot, and thinking "Oh PLEASE dont let me drop it! PLEASE dont let me drop it! I CANT AFFORD to DROP IT!"

And of course.... sods law says... you thrash that little single, waiting for it to go 'pop'... it will keep on going..... terrified of cracking the plastic on an R125? Well, Murphey ENT going to let THAT opportunity for mischief pass him by very long!

I really want to see this bike on the road.... another derelict finding redemption. Another owner discovering the joy of creating what they ride.
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Cafe? Indicators & stuff? much of a much, usually one bolt fitting, and where there's a will there's a way!

Front forks & headlamp stays? Universal ones can usually be packed out with strips of rubber cut from the old inner tunes you take out of them old tyres!

BUT here and now, multimeter, get the wiring all buzed out, clean all the contacts and connectors in the switches and everything; make sure your flasher is working, and that earths are earthing....

That is where the attension to detail will pay off, and reliability is most likely to be found. Wiring is a nif-naff niggling ball-ache that takes lots of time, and sees little progress, but well worth the effort.

If it has the Super-Dream tail lamp.... plastic casing with metal tube bulb holder.... DRILL through the casing, and put an M4 bolt through to make a direct earthing point, and solder it in place. Original earting arrangement is an ABORTION!

DONT be tempted to use generic crimp connectors for halfords ANYWHERE.... on old oxidised wire, its a recipe for faults and failures and the connector force is so often greater than the crimp force that they pull straight back off the wire anyway!

Go to Vehicle Wiring Products and order a couple of bags of 'Japanese standard' bullet connectors and sockets, and the insulation for them; get a good butane soldering iron and SOLDER them on where needed to get good electrical AND mechanical joints.

Get a roll of green wire and some ring terminals too, to make up 'garanteed' earth returns to the battery, from the common earthing point in the head-lamp, the chassis earth, and the 'one wire' components like the indicators... just saves answering SO many silly questions later!
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[symonh2000]

[caferacer]

WOW!!! Amazing post, thanks Teflon-Mike!!!!!!!

[Pol Anorl]

Oh god! teffers is having a mini stroke looking at this thread, his heads working overtime! a thread about cb125s, get 5 replacement keyboards at the ready for when he wears off the keys replying.
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GOOD GAME BODYGUARD: https://i.imgur.com/8WePGgf.jpg
20:30:37 Pyro.: I don't sort of like men, I take every advantage to choke on dick.
Jewlio Iglesias: You live in Liverpool - Chances are, the front door has already been kicked off the hinges

[Teflon-Mike]

[caferacer]

[TheSmiler]