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Honda CB 125S/J

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

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.