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Honda CB 125S/J

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Make Model

Honda CB 125S/J

Year

1979 -

Engine

Four stroke, single cylinder, SOHC, 2 valve

Capacity

124 cc / 7.6 cu-in
Bore x Stroke 56.5 x 49.5 mm
Cooling System Air cooled
Compression Ratio 7.4:1

Induction

Keihin 24mm slide type manual choke

Ignition 

Battery & coil
Starting Kick

Max Power

14 hp / 10.3 kW @ 10000 rpm 

Max Torque

9.9 Nm / 7 ft-lb @ 9400 rpm
Clutch Multi-disc, wet

Transmission 

5 Speed
Final Drive Chain
Gear Ratio 5th 9.46  /  4th 11.10  /  3rd 13.72  /  2nd 17.81  / 1st  26.20

Front Suspension

Oil-damped telescopic forks

Rear Suspension

Swing arm, dual shocks

Front Brakes

Drum

Rear Brakes

Drum
Wheels Steel, Wire-Spoked

Front Tyre

2.75 -18

Rear Tyre

3.00 -17

Dry Weight

95 kg / 209 lbs
Wet Weight 105 kg / 231 lbs

Fuel Capacity 

9.5 Litres / 2.5 US gal
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When the compiler was asked to advise on a replacement as office hack for a troublesome 250 two-stroke from eastern Europe he suggested that a 125 Honda might be faster, more economical, more reliable, and possibly a little less expensive.

This incident occurred in 1972, in the first year of the 125S. The model has continued in the Honda range, with minor changes to specification and suffix letter, and seems likely to become more important in the UK during the Sec-restricted learner phase.

A 1976 125J is representative of the line. Though more sporting than the S, and with its role as commuter bike presumably delegated to the newly introduced pushrod ohv CG125, the 125J showed few large-scale changes compared with the original. Most obvious was the front disc brake, which replaced a 6in-diameter drum unit.

The handlebar was changed for a flatter type, the exhaust silencer enlarged and re-angled, the fuel tank reshaped. Internally, the cylinder head had been reworked and the carburettor choke size increased by 2mm to raise power by 1 -2 bhp, to complement revised gear ratios. The effect was to make the J a little faster, compared with the earlier model, but more sluggish in the critical 0-40 mph zone. Fuel consumption remained outstanding, with 80-100mpg available depending on riding methods.