Honda XL125S Specs and Info (1979 to 1985)


1979 Honda XL125S

Honda XL125S Specs…..

The Honda XL125S was a road legal off road motorcycle manufactured between 1979 and 1985.
The XL125 S had a reliable 4 stroke, 124cc, single cylinder, air cooled engine. The XL125S had a few improvements over the earlier XL125 models including electronic CDI, 6 speed gearbox and rubber mounted indicators, making them less likely to stop working in the event of a fall.

A little bit about the Honda XL125 S…..

Basic model info…

Manufacturer: Honda
Model: XL125S
CC: 124cc
BHP: 12.5
Engine type: Single cylinder, air cooled (4 stroke)
Years in production: 1979 to 1985
Style of bike: Off road (road legal)
Insurance: Get a discount on your insurance at

Engine and gearbox specs…..

Displacement: 124 cc (7.57 cubic inches)
Engine type: Single cylinder
Stroke: 4 stroke
Bore×Stroke: 56.5 x 49.5 mm (2.2 x 1.9 inches)
No. of cylinders: 1
Cam shaft configuration: OHC (overhead cam)
Compression ratio: 9.4:1
Cylinder compression pressure: 11 to 14 bar (160 to 203 psi)
Valves: 2 valve (2 per cylinder)
Spark plug: NGK DR8ES-L (x1)
Spark plug gap: 0.6 to 0.7mm
Firing order: Erm….It’s a SINGLE cylinder! 😀
Engine oil: 10w40 API SE or higher
Engine oil drain bolt location: Bottom/left side of the engine casing
Oil filter type: Screen / mesh
Cooling system: Air cooled
Clutch: Wet (oil immersed) multiplate clutch
Clutch operation: Cable
Clutch cable operation: Lever (on handle bar)
Clutch lever free play: 10mm

Note: Clutch levers are fairly cheap, if you need to get one get a few as there easily damaged if your playing about off road!
You might also need a clutch holding tool if your replacing the clutch.

Gearbox: 6 Speed manual (1st gear down, 2nd to 6th gears up, neutral between 1st and 2nd gears)
BHP: 12.5 bhp
Top speed (claimed): 62 mph….Ish! (100.0 km/h)

Note: Top speeds are very APPROX!! as it’s not unusual for these figures to be slightly inflated by the manufacturer to help sell more bikes! 😀

Piston ring to cylinder bore clearance: New: 0.010 to 0.040mm / Max 0.100mm
Valve clearance (inlet): 0.05mm (when cold)
Valve clearance (exhaust): 0.05mm (when cold)
Idle speed: 1,300rpm (+/- 100)
XL125S front
Front/side view of a 1979 Honda XL125S in black

Final drive stuff…..

Final drive: Chain
Front sprocket: 14 teeth
Rear sprocket: 47 teeth
Chain pitch/length: 428 pitch / 120 links
Chain free play: 30 to 40mm
Chain stretch limit: 518mm over 40 links
XL125S in black
Rear/side view of a 1979 Honda XL125S in black

Carb, fuel and oil stuff…..

Fuel system: Carburetor
Fuel tank capacity: 6.8 litres
Fuel type: Unleaded petrol (91 octane grade – aka standard, unleaded petrol from your local garage)

Note: The XL125S had an alloy cylinder head, which means you can use unleaded petrol without any problems (years ago, lead was added to petrol as a lubricant for cylinder heads made from cast metal)

Carb make: Keihin (1x)
Carb type: PD21A/C
Pilot screw opening: 2.5 turns
Engine oil: 10w40 API SE or higher
Engine oil drain bolt location: Bottom/left side of the engine casing
Oil filter type: Screen / mesh

Note: The oil is filtered by a cylindrical screen which can be cleaned not by a conventional replaceable type oil filter

XL125S clocks
Clocks and switches on a Honda XL125 S

Electric stuff…..

Ignition type: Electronic CDI
Starter: Kick start
Electrical system voltage: 6 volts
Electrical system capacity: 4 amps/hour
Alternator output (max): 4.5 amps (@ 8000 rpm)
Spark plug: NGK DR8ES-L (x1)
Spark plug gap: 0.6 to 0.7mm
Spark plug ignition: 1 x coil
Coil primary resistance: 0.2 to 0.8 ohms
Coil secondary resistance: 8000 to 15000 ohms
Pick up coil resistance: 20 to 60 ohms
Battery: 6N4-2A-4


  • The 6N4-2A-4 battery is a 6 volt, 4 amp/hour battery and is length: 70mm width: 70mm height: 95mm in size (more info…).
  • Also…… Avoid buying the cheapest of the cheap type batteries online as they have a horrendous failure rate (and they can be a bug!er to post back when it fails.
XL125S battery
6 Volt battery for a Honda XL125 S (6N4-2A-4).

Shocks, brakes and wheel specs…..

Front wheel type: 21 inch spoked wheel
Front tyre size: 275-21 (same as 2.75-21)

Note: There are 2 different formats for imperial sized tyres, but both variations are normally the same size (for example 275-21 and 2.75-21 are both the same size).

Front innertube size: 250/275/300-21

Note: Because of their stretchy nature, motorcycle inner tubes usually fit a few different sizes (widths) of tyre because they can stretch to fit. So a 250/275/300-21 tube and a 275/300-21 tube would both fit a 275-21 sized tyre.

Front tyre pressure: 21psi (1.5 bar)
Front wheel spindle torque: 45nm
Rear wheel type: 18 inch spoked wheel
Rear tyre size: 410-18 (same as 4.10-18)
Rear innertube size: 325/350/410-18
Rear tyre pressure: Solo: 21psi (1.5 bar) / With pillion: 25psi (1.75 bar)
Rear wheel spindle torque: 70nm
Front brake: Drum (130mm)
Front brake pad: EBC H304 (1x)
Rear brake: Drum (120mm)
Rear brake pad: EBC H304 (1x)
Front suspension: Telescopic forks
Front fork stanchion diameter: 31mm
Recommended fork oil: 10w fork oil
Fork oil volume: 160 cm3 (per fork)
Rear Suspension: Twin shock
XL125S clocks
Right/back view of an XL125 s in black

Weights, measures ‘n stuff…..

Seat height: 818mm (32.2 inches)
Kerb weight (with oils, fluids etc): 106 kg (234 lbs)
Fuel tank capacity: 6.8 litres
XL125S left side
Left side view of an XL125S

Useful torque settings…..

Front wheel spindle: 45nm
Rear wheel spindle: 70nm
Cylinder head: 18 to 20nm
Magneto / flywheel: 40 to 60nm
Camshaft sprocket: 8 to 12nm
Clutch hub: 40 to 50nm
XL125S right side
Right side view of an XL125S (note the homemade side panel, right side panels for these bikes are rare as hens teeth for some reason!)

Service stuff…..

Servicing your bike? You’ll need an XL125 workshop manual…
Engine oil
Engine oil change frequency: Every 6,000km (approx 3,728 miles) or 12 months
Engine oil: 10w40 API SE or higher
Engine oil capacity: 900ml
Engine oil drain bolt location: Bottom/left side of the engine casing
Oil filter type: Screen / mesh
Chain drive
Final drive chain frequency: Now repeat after me… ‘I MUST LUBE MY CHAIN LITTLE AND OFTEN!!’
Chain and sprocket size: 120 link / 428 Pitch chain
14 Tooth front sprocket
47 Tooth rear sprocket
Fork oil
Recommended fork oil: 10w fork oil
Fork oil volume: 160 cm3 (per fork)

Frame number location…..

The frame number is usually stamped onto the right side of the headstock (the front part of the frame just below the handle bars).

Useless stuff…..

Although not a patch on modern standards and speeds, the XL125S was a good, reliable bike in it’s day and it’s fairly common to see them used as ‘field bikes’ now.
The XL125 S used the newer, slightly larger (124cc) cc engine and benefitted from a CDI ignition.
The bike also had a 6 speed gearbox which made the narrow powerband (7,000 to 10,000rpm) much more useable.
The model remained basically the same during it’s life (1979 to 1985) with changes to colours and graphics.

Buying advice…..

The XL125S isn’t a bad little bike for playing around off road, although it is a plodder so your unlikely to be competing in the Paris Dakkar rally on one!
There are a few about so there’s tons of ‘barn find’ and ‘field bike’ type bikes around. Unless you know what your doing or just looking for a pure off road (i.e. not road legal) hack it’s best to stay away from them as without the paperwork there likely to either have been nicked at some point in there history or no longer on the DVLA vehicle records.

The engines are fairly bullet proof and basic spare parts are available, but exhausts tend to rot and exhaust spares are rare (and expensive when they do come up!). However, the exhaust system is fairly simple so it wouldn’t be too difficult for a reasonably competent fabricator/welder to knock something up cheap.
The other odd thing about these bikes is right side panels, which are rare as the proverbial rocking horse poop for some reason?

The only other thing to consider when buying one is the age. The youngest of these beasties will be over 30 years old now, so if your buying one give it a good check over, especially rear shocks, fork stanchion condition (helps if the forks have had fork gaitors fitted), handle bar switches, ignition, battery etc.

Happy biking 🙂

Sources / Thanks to / Useful XL125 S sites:

XL125 article on Wikipedia
Rock Oil for the oil info

29 thoughts on “Honda XL125S Specs and Info (1979 to 1985)”

  1. I also have a 1979 Honda XL 125s. Perfect working condition. I am looking for the right side cover to make it complete. Do you have one? Know where I could find one? Thanks.

    1. Unfortunately we don’t have one, the right side panels are as rare as rocking horse poo (if you’ll pardon the expression!). Very difficult to come by for some reason?

  2. Hi is the front wheel and spokes in good condition. Is the engien a good runer and not smokey as I need bot these parts engien adn front wheel how much and postage to Birmingham ta Iain

  3. Hello, Im after the rear light assembly but depends on condition of the mirror inside , how much please cheers glynn

  4. hello have you got the exhaust header collar that the bolt holes go through for the down pipe and the collets and how much cheers thanks

  5. With regards to the xl125s right side cover. (I know its a little out of date) but for future reference, I have a side cover that will be getting replicated. I also have moulds for other classic bikes, cb750c, cb900/1000c cb700s nighthawk, cb450sc nighthawk, cb550sc nighthawk, gl1200 goldwing left side covers. I also have many others too, Yamaha xj550 SeCA (both left and right) ALL AVAILABLE AS REPLICAS.

    Hope this may help anyone.

    1. Hello, I could use a right hand side panel for my 1979 XL 125. How much for the panel and shipping to Canada? Thanks


  6. hi there, have you got a engine sproket cover,and also the full front @back light assembleys,(everything) indicators clocks etc?

    1. It depends if your looking to do a full restoration back to original or just want to get it going as a cheap hack?

      Generally, they are fairly simple and straightforward bikes so shouldn’t cost bucket loads or require alot of specialist work to get going

  7. Dragged my old 82 xl125s out of mum’s garage recently. Hasn’t been started in 20 years. Put some fresh petrol in it and a couple kicks and it’s going. This info has been a big help as it needs some tic from me and my brother Jerry rigging it when we broke stuff.

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