The KX125 won three straight AMA 125cc National Championships in the hands of superstar Ricky Carmichael from 1997-99 and Kawasaki soon set to work upgrading the production bike.
Kawasaki KX125 (1999-2001)
In 2001 Kawasaki released a new version that had been reworked from top to bottom. The liquid-cooled, two-stroke engine got a new cylinder head with a reshaped combustion chamber to boost compression. A new piston complemented the reshaped head and ran tighter tolerances to the electrofusion-coated bore.
A new Mikuni TMX 36mm carburettor was added. This carby put the needle closer to the intake while a new float bowl shape allowed the carburettor itself to be positioned closer to the crankcase without interfering with the clutch actuating arm. Reshaped crankcases increased primary case compression for the mixture, with revised ignition timing to fire it up. At the reshaped exhaust port, the Kawasaki Integrated Power valve System (KIPS) governor had heavier bearings, new bearing cups and stronger springs to prevent power valve flutter. The KIPS, which varied exhaust port timing according to engine speed for a broader powerband, opened more quickly for increased mid-range power. A shorter muffler reduced weight and enhanced mid-range response.
A lighter flywheel complemented the other engine changes for quicker engine response. Kawasaki offered three accessory flywheels of various weights to fine tune engine performance to suit track conditions and riding styles. The final engine improvement for 2001 was a new shift drum holder that was similar to that used on the KX250 and improved shift feel.
The high-tensile steel perimeter frame helped centralize mass and provided a long, flat seating position. To reduce weight for 2001 the mounts and bolts holding the fully-adjustable, bladder-type inverted cartridge fork were redesigned and the aluminum steering stem was tapered. A new front brake master cylinder was added and operated a dual-piston caliper with larger diameter pistons.
The rear suspension used Kawasaki’s Uni-trak linkage that progressively increased damping and spring rates on the shock as the suspension compressed. The shock got revised damping settings in 2001 to match the new spring and the lower linkage bolts where hollowed out to reduce unsprung weight.
For 2001, the engine improvements included a new head, piston and cylinder, a new reed valve block, new crankcases and a new Mikuni TMX carburetor which pushed the power output up to 38hp (29.1kW).
The front caliper on the 2001 model got 27mm pistons instead of the previous 22.65mm ones and the master-cylinder piston size was increased to 11mm from the previous 9.52mm.
The front end ran a 46mm upside-down, dual air-chamber fork with 305mm of travel, 18-way compression and 18-way rebound damping adjustment. The rear end ran a Uni-trak set-up with adjustable preload, compression and rebound damping.
The frame was a high-tensile steel perimeter frame with aluminum subframe.
It sounds crazy, especially when we are riding four strokes weighing over the 100kg mark but back in 2001 the KX125 weighed in at a claimed 87kg dry.
– 1999-2001 Suzuki RM125
– 1999-2001 Honda CR125
– 1999-2001 Yamaha YZ125