||There are so many good web sites on the Internet that I used to fix up my bike that I had to collect them all together for the benefit of others. Thanks to so many helpful web sites! If you know of a site that would be helpful in restoring a 1980 Honda CB125s please let me know.
The older Honda CB125s is unique in that it runs on a 6 volt electrical system coupled with a 6ah battery. Proper lighting is critical to safety.
Turn Signal Indicator Relay
My turn signal indicators were working erratically, sometimes blinking and sometimes not. Take the black cover off and you'll see a contact switch. Mine was covered with carbon deposits, which I scraped away with a small screwdriver followed by a good spray of electrical contact cleaner. Now the indicators work very well, and even sound with a nice tic, tic, tic. A replacement turn signal relay costs $44.44CAD.
Replacing the Exhaust Gasket
Once the bike started up I noticed that exhaust smoke was coming out between the engine and the exhaust muffler pipe. To repair this you need to replace the exhaust gasket.
- remove the 2 nuts at the exhaust outlet, the plate that attaches the exhaust pipe to the frame, connected by 2 nuts facing the rear tire, a bolt through the swingarm and a nut from underneath. That's 6 nuts in total. Removal of the right footpeg makes it a little easier. You do not need to remove the seat, gas tank or side covers.
- Remove the exhaust pipe flange. It is a one piece oval thick piece of metal.
- Remove the 2 piece split collets, thick metal pieces on either side of the bolts. They will drop off the pipe once the oval exhaust pipe flange is removed. They are semi-circular with a lip. These 2 pieces fit on between the bolts. Ensure that they also fit into the exhaust pipe flange, which is partly inset for these 2 metal collets for a tight fit. I had to grind mine down on the edges to ensure a tight fit into the exhaust pipe flange.
- Remove the exhaust pipe and muffler.
- Using a screwdriver you should see the round exhaust gasket. It's probably squished flat. Replace this.
- Reassembly will take more time. The back brake lever needs to be pressed to get the pipe into place. From the engine the order of parts is: exhaust gasket, exhaust pipe and muffler, 2 piece collets, exhaust pipe flange, 2 nuts. Hand tighten everything until you've fitted the rear part of the muffler.
- Locktite all nuts
- Parts: exhaust gasket pn 18291-mn-650 $2.40CAD
Air Filter Replacement
Remove/replace the foam air filter. If dirty clean with solvent. Pour 10w30 oil into the filter and gently squeeze excess out. Install air filter.
Parts: foam air filter pn 17213-383-670 $12.50CAD
The rim sizes written on the rims are: 18 x 1.4F, 17 x 1.6R but when measured they are 18 x 2.1F, 17 x 2.3R The recommended tires are 2.75 x 18F, 3.0 x 17R. The max tire you can put on are 3.5 x 17R, 3.5 x 18F. I'm not sure how this will affect handling.
There are few tires available for this bike. Cheng Shin is the only option I could find in North America. C265 3.00 x 17R, C180 3.25 x 17R, C223 2.75 x 18F, C904 90/90-18F.
In Britain, Pirelli makes a City Demon in 90/90-18F, 3.00 x 18F, 3.0 x 17R
If you know of any other tires please let me know. The following tire manufacturers have NO tires that will fit: Pirelly North America, Bridgestone, Avon, Dunlop, Metzeler, Michelin.
eMail me and we can exchange hints and tips.
CB125 General Info
General Bike Links
Honda Part Numbers
- Carb float bowl gasket and set: pn 16010-312-004, substitute pn 16010-107-305 $9.46CAD
- exhaust gasket pn 18291-mn-650 $2.40CAD
- axle castle nut torque 40-50Nm/29-36ft-lb pn 90305-169-00 $3.18CAD
- kickstart lever ID 0.6"/15.24mm pn 28300-439-010 $99.47CAD buy it off eBay instead
- clutch cable pn 22-870-383-670 $17.27CAD
- spark plug NGK D8EA $3.90 gap 0.6-0.7mm/0.024-0.028"
- foam air filter pn 17213-383-670 $11.74CAD
- spark plug cap NGK $5CAD
- engine muffler stud 6x36 pn92900-060280B $0.94CAD
- hex nut for engine muffler stud 6mm pn 90230-087-000 $1.88CAD
- collar exhaust joint (comes in a pair) pn 18233-330-00 $2.96CAD
- Locktite every nut on your bike or you'll be buying these parts
- petcock pn 16950-107-005
- fork seals 27mm x 39mm x 10.5mm pn 90756-149-841
- Honda 100-350cc OHC Singles, 1969-1982, Clymer, M315, 1983 $40CAD
- Honda CB100N & CB125N Owners Workshop Manual, Haynes, 1990, Martyn Meek: Covers 99cc 1978-1980, 124cc 1978-1980 bought off eBay UK
Retailers/Salvage Yards - Toronto