Kawasaki 125 Dirt Bike (KX) Specs and Review

At the time of its launch, the Kawasaki 125 Dirt Bike was considered a formidable contender of the 125-class. Its 1984 redesign marked the beginning of the KX™ lineup, re-establishing credibility – an excellent comeback for the Japanese manufacturer after experiencing a low in sales in the ’70s and early ’80s. A powerful dirt bike with a lot of promise, the KX 125 placed Kawasaki back on the map of MX racing.

The Kawasaki 125 Dirt Bike was a 124-cc off-road bike produced by Kawasaki from 1974 to 2009. This seemingly straightforward, enduro-style machine featured an all-new design that got the ball rolling for higher-displacement bikes that eventually went on to win Baja championships.

Ingenuity was always a major selling point for Kawasaki. And yet, it took almost a decade for Team Green to realize the same for the KX 125.

Luckily, things were not yet too late, and the bike’s major overhaul in 1984 put it in favor of consumers and enthusiasts alike for another 25 years.

Read on, and discover this and a whole lot more about the Kawasaki KX 125 in this article.

Green Dirt Bike on Dirt Track

About the Kawasaki KX 125

The Kawasaki Dirt Bike 125 is a renaissance of the 1983 Quacker, known for its massive horsepower but severely criticized for its design deficiencies. During its construction, the Japanese manufacturer got rid of the unwieldy chassis, harsh forks, flimsy metal, and unimpressive styling of its predecessor, keeping only two strong points – the front disc brake and the powerful motor. The KX 125 was then redesigned after the Works Machine of Jeff Ward (retired Kawasaki motorsports champ and IndyCar racer).

A Notch Higher

Key enhancements of the Kawasaki 125 2Stroke are reflected in its framework, motor, transmission, and overall reliability. The chassis was configured with a shorter wheelbase and a steeper head angle, making for faster steering input reaction and improved handling when climbing.

Larger tubing in critical areas and increased gusseting at the swingarm pivot made the new frame lighter but more robust. Team Green engineers reinforced the crankcases and increased the surface mating area to resolve issues with air leaks.

Other updates included wider-toothed gears, new friction plates with embedded radial grooves for the clutch, internal porting, and all-new expansion chamber and ignition. Improvements made to the bike’s cooling system were particularly notable.

Compared to the previous-year version, the 1984 KX received a longer single-sided radiator and enlarged water passages, addressing overheating issues and resulting in a 29% cooling capacity increase.

As a result of these changes, the Kawasaki Dirt Bike 125 felt more like a 150-cc machine and turned from an MX bench warmer to a powerhouse. It pulled earlier on the tracks and did so with more authority than its same-displacement counterparts. The new motor also made the bike suitable for nouveau riders and not just pros.

That One Handicap

While the KX 125 was considered best in power output and placement, its suspension system still screamed improvement. Unfortunately, tweaks done on the bike’s suspension components were not enough. The slightly stiffer springs still felt underdamped for intermediate to pro drivers.

Due to large jumps still ending in crash landings and complaints about harsh spikes in the mid-stroke, the Kawasaki KX 125 was considered as having the worst front-end performance of all 125-class bikes in 1984.

This is not to say that the inadequate suspension system was its only long-standing issue. Front disc brakes were still prone to leaks and in need of constant bleeding. Plastics continued to have a propensity to break, especially for hard-ridden or competition wheelers – among other things.

But despite falling short on these aspects, the Kawasaki 125 Dirt Bike was, nonetheless, a solid and reliable machine. Its setbacks were not impactful enough to derail the bike’s rise to fame as the “Ruler of the Roost.”

Kawasaki 125 Dirt Bike Specs & Features

Engine

A liquid-cooled, 2-stroke single-cylinder power mill with high-tech carbon fiber reed valves powers the Kawasaki 125 Dirt Bike. It has a bore-stroke ratio of 54 × 54.5 mm (2.13 × 2.15 inches). Engine displacement is 124 cm³ (7.6 cu in³), while the compression ratio is 10.6:1 (low speed)/8.1:1 (high speed). A 34-mm Mikuni carburetor with a flat bottom R-slide handles the air-fuel mixture. For later-year models, carb size was upgraded to either a Keihin PWK36S or a Mikuni TMX38X.

The above engine configuration lends to a Kawasaki 125 Dirt Bike top speed of 55 – 60 mph (88 – 96 km/h), 26.5 Nm (2.7 kgf-m, 19.5 ft-lb) @ 2,700 RPM maximum torque, and 40.49 hp (29.6 kW) horsepower. Later-year versions equipped with the 38-mm Mikuni carb rendered a top speed of 75 mph (120.7 km/h), 41.04 hp (30.6 kW) @ 11,500 RPM horsepower, and a maximum torque of 27 Nm (2.75 kgf-m, 19.92 ft-lb) @ 10,500 RPM.

Fuel & Lubrication

Fuel tank capacity is 8.2 L (2.2 US gal) of unleaded gasoline with a minimum rating of PON 87/RON 91. Thanks to the KX 125’s engine configuration, the bike offers a decent fuel economy of 60 mpg (3.92 L/100 km). The manufacturer recommends fuel variants containing < 5% MTBE (Methyl Tertiary Butyl Ether), < 10% ethanol, or < 5% methanol. But in the event engine knocking or pinging occur, switching fuel brands is advised to prevent severe engine damage.

Additionally, it requires 0.7 L (0.74 US quart) of K-Tech 2-stroke oil or its equivalent. The recommended oil viscosity is SAE 10W-40 with a minimum API grade of SJ meeting JASO T903 MA, MA1, MA2 standards. Depending on ambient temperature, you may go for SAE 10W-30, 10W-50, 20W-40, or 20W-50. Always check the manual when using alternative lubrication on the KX 125. Otherwise, you may encounter poor running or loss of power at high speeds if the viscosity grade is too high.

Green 2005 Kawasaki KX125 Dirt Bike

Drivetrain

A manual (wide-ratio) 6-speed constant mesh return system (left-foot operated) and a wet, multi-disc clutch assembly deliver power to the wheels. A 520 O-ring chain (with 112 links + joint) handles wheel spin. The Kawasaki 125 Dirt Bike’s wide-ratio transmission is responsible for its ability to pull ahead of the competition on racetracks and produce massive power with fewer revs, putting it on par with 250-cc wheelers. For ’92-’93 models, front and rear sprockets changed from 13/51T to 12/49T (4.08), further improving acceleration.

For reference, the stock gear ratios are below:

Primary Reduction Ratio3.200 (64/20)
Final Reduction Ratio3.923 (51/13)
Transmission Gear Ratio (1st)2.384 (31/13)
Transmission Gear Ratio (2nd)1.857 (26/14)
Transmission Gear Ratio (3rd)1.529 (26/17)
Transmission Gear Ratio (4th)1.294 (22/17)
Transmission Gear Ratio (5th)1.125 (27/24)
Transmission Gear Ratio (6th)1.000 (25/25)
Overall Drive Ratio12.553 @ Top gear

Ignition

The 125-cc Kawasaki KX has an electronic CDI (Capacitor Discharge Ignition) and a primary kick-start system waking it up. The vehicle’s overall charging system is a flywheel magneto, which also powers up electronic accessories. Ignition timing is 13° BTDC @ 9,710 RPM (initial “F” mark).

All models have a 130-CCA 12V (6 Ah)/10 HR YTZ7 battery (view on Amazon) with dimensions of 113 x 70 x 105 mm (4.44 x 2.74 x 4.12 inches – L x W x H). They require an NGK BR9EIX spark plug with a 0.7 – 0.8 mm (0.028 – 0.031 inch) gap and tightening torque of 27 Nm (2.8 kgf-m, 20 lb-ft) – except for the ’97 model, which has an NGK BR9EVX plug. European releases have either an NGK R6918B-9 or NGK BR9ECMVX plug type.

Tires & Brake

The front and rear aluminum wheels use Dunlop® tires. You can swap out the front tires for Maxxis M7304D Maxxcross Desert IT Tires (view on Amazon). Similarly, rear tires can be changed to Dunlop Geomax MX33 Tires (view on Amazon) – perfect for soft-to-intermediate terrain.

Recommended tire pressure is reliant on track conditions – 80 kPa (0.8 kgf/cm², 11 psi) for muddy, sandy, or slick terrains and 100 kPa (1.0 kgf/cm², 14 psi) for pebble-laden or hardpack surfaces. The right amount of pressure will either increase the tread surface on the ground or help prevent punctures or tire damage. Finally, a 220-mm (8.7-inch) front disc with dual-piston calipers and a 200-mm (7.9-inch) rear disc provide stopping power and complete the KX 125’s tire-and-wheel assembly.

Suspension

The front suspension consists of conventional 43-mm Kayaba forks (other model years have a shorter 36-mm cartridge fork). At the back, the same Uni-Trak® linkage rear suspension used on the ’83 125-cc bike and KLX 300s were used but slightly revised from its original configuration to offer less progression.

The rear suspension was then mated to aluminum Kayaba shocks with a new bladder design (as opposed to the de Carbon system used by the Quacker), lending to improved fade resistance, wheel travel, and smoother handling. Both front forks and rear shocks offer a generous amount of wheel travel – 300 mm (11.8 inches) and 310 mm (12.2 inches), respectively. They are also compression- and air-adjustable. However, they had no adjustment for rebound.

Green 1999 Kawasaki KX 125 Dirt Bike

Dimensions

The overall dimensions of the Kawasaki 125 Dirt Bike are 2,155 x 825 x 1,200 mm (84.8 x 32.5 x 47.2 inches – L x W x H). Machines released in Europe only differ slightly in measurement from those in North America – at 85.2 x 33.1 x 49.8 inches. Ground clearance is 340 mm (13.4 inches), while the wheelbase measures 1,455 mm (57.3 inches) ± 2%. The saddle sits at a height of 930 – 940 mm (36.6 – 37 inches). Dry weight is 87 Kg (192 lbs).

Exterior

It has a tubular semi-double-cradle steel frame (with a 27.5° caster angle, 100-mm/3.9-inch trail, and 45° steering angle). Standard Kawasaki 125 Dirt Bike parts include handlebars, grips, chain and fork guards, and front and rear fenders. Since the bike does not have a skid plate, getting a Devol Skid Plate (view on Amazon) will help protect the underside of your vehicle.

As for styling, Kawasaki adopted the polished look of Jeff Ward’s Works Machine – all except the orange saddle, which was replaced with a more tasteful blue to fit the bike’s overall aesthetic. Aside from the color, the seat was also reshaped to sport an up-to-tank design. This change complemented the slimmer tank-and-shroud combo, making sliding forward less obtrusive and easier. The buzzard-beak front fender became more rounded and had a thin alloy brace underneath that prevented it from cracking if weighted down with mud.

Kawasaki KX 125 Price

The list price of the KX 125 ranges from $4,949 to $5,099 for post-2000 models. However, resources for the MSRP of older KX versions can be a bit obscure. Nada Guides data indicate average resale values for all models only until 2005, leaving out the last three production years of the two-wheeler. Pre-1985 models keep their value pretty well, which is currently almost double their original list prices. Conversely, later-year versions of the bike can go as low as $250.

Year – Trim – Model NumberRetail/Trade-In Values
1974 – 1977 Kawasaki KX125/A3$690 – $7,095
1978 Kawasaki KX125-A4$1,110 – $8,725
1979 Kawasaki KX125-A5$750 – $7,375
1980 Kawasaki KX125-A6$750 – $4,645
1981 Kawasaki KX125-A7$990 – $6,670
1982 -1984 Kawasaki KX125-B1/B2/C1$750 – $4,645
1985 – 1991 Kawasaki KX125-D1/E1/E2/F1/G1/H1/H2$750 – $3,990
1992 – 1993 Kawasaki KX125J1/J2$250 – $1,830
1994 – 1998 Kawasaki KX125K1/K2/K3/K4/K5$250 – $1,975
1999 – 2002 Kawasaki KX125L1/L2/L3/L4$345 – $2,045
2003 Kawasaki KX125M1$480 – $630
2004 Kawasaki KX125M2$615 – $810
2005 Kawasaki KX125M3$775 – $1,020

Online, the saleability of the 125-cc bike seems to be overshadowed by the greater popularity of its successor, the Kawasaki KX250F. You could find this pre-loved classic in good condition if you go to known trader sites or directly to private owners. Expect secondhand prices to fall within the same range as the above. Anything beyond $4,000 would usually come with mods, lights, or performance-enhancing parts.

From Off-Road to Street-Legal

While the Kawasaki 125 Dirt Bike is undeniably an off-road machine, consumers nowadays buy the two-wheeler and turn it into a city ride. This should come as no surprise, as enduro-style bikes have recently become a top choice for recreational and city driving. This section explains how to convert your off-pavement bike to a daily commuter.

DOT-Compliant Headlight

There are three features your headlight should have to be compliant:

  • Have high and low beam function (and preferably actuated via an easy-to-reach switch)
  • Be clearly visible but should not be blinding to drivers or oncoming traffic
  • Provide ample light distribution for both day and night

You can choose from halogen, HID, or LED lights for your headlamps. However, note that halogen lights draw on your bike’s electrical system more than LED does. Additionally, you will need to have a charging system to go with your battery. If you stick to halogen, make sure to get a new stator to help power the lighting system you will equip the bike with.

Whichever you choose, I strongly suggest using battery-powered lights to avoid encountering dimming of lights when running low on the RPMs.

Brake Light & Taillight

Your brake/taillight should ideally be connected to a battery and remain lit for a minimum of 20 minutes. Its light should be visible enough to notify other drivers that you are slowing down or attracting attention when riding during the day. Only a single motorcycle brake light/taillight is required in certain states. To be certain, research your state/township guidelines on brake and taillights.

When installed correctly, the taillight activates when both the rear brake pedal and front brake lever are engaged. A banjo-bolt switch ensures this takes place by using extra pressure in an engaged brake line. Meanwhile, mechanical switch options work best for drum brakes. While you are at it, buy an aftermarket bracket-fender combo for a finished look after installing the necessary lighting.

Rearview Mirror

Thankfully, mirrors go well with the rugged look of the dirt bike. While only some locations require one working mirror, it would make sense to install two. If you find stem mirrors distasteful, you may opt for low-profile wide-angle mirrors or bar-end mirrors for looks. These options have a lower profile than most types and still do a decent job eliminating blind spots on both sides of your dirt bike.

Turn Signals

Installation of flashers/blinkers may be skipped in some states/areas if you use hand signals. But to side with caution, having blinkers with a self-canceling feature is better as it lets you focus on the road when making a turn. Refer to specific state rules when mounting front and rear turn signals. Furthermore, take note of the recommended height and gap between the turn signals during installation.

DOT-Approved Tires

Equipping the KX with DOT-certified tires is a must, as the stock rubber on the bike is ill-suited for riding on pavement. Tires marked with the letters DOT on their sidewall, on the other hand, contain extra layers of rubber and are highway-speed rated. Supermoto builds are a growingly popular way of converting an off-road vehicle into a dual-sport bike. And as long as sportbike tires fit on your bike’s rims, they may be swapped for stock rubber.

Horn – The two biggest requirements when installing a horn is as follows:

  • It must be audible from at least 200 feet away
  • It must be electric (some states reportedly allow non-electric horns to pass inspection)

License Plate Bracket

Kits including a replacement fender with a license plate holder and light are available online. Some options do not include a replacement fender. Whether you mount your license plate vertically or horizontally, a light will be necessary to make the plate clearly visible. Mounting an inexpensive LED strip above the license plate makes this possible.

Other road-legal requisites include a muffler, reflectors, complete digital instrumentation, correctly vented crankcase, and other EPA-friendly emission controls. Installing a fan or adjusting gearing for street use may also be required. Depending on the condition of your bike (if you have a secondhand wheeler), you may have to do some suspension and top-end work, as well as a frame restoration.

The most challenging thing about getting your KX 125 legal on the road is getting the paperwork/sign-off from your local motor vehicle office. For more requirements specific to certain U.S. states, check out this article on the Honda XR650R.

About Kawasaki

Kawasaki Heavy Industries, Ltd. is the maker of Kawasaki 125 Dirt Bike and is widely known for its off-road vehicles, motorcycles, side x sides, and watercraft. The Japanese firm is responsible for creating some of the most powerful and innovative machines in the market. Additionally, it is a respected force in the world of motorcycling.

The company has been on and off the Enduro motorcycle scene for the past few decades. But with its recent product offerings, the riding community cannot help but look forward to greater things from its product lineup. Kawasaki’s priorities continue to improve aerospace and energy systems, hydraulic machinery, ATVs, motorized vehicles, transit, and personal watercraft.

Conclusion – Kawasaki 125 Dirt Bike Review

Throughout its production, the Kawasaki 125 Dirt Bike continued to receive upgrades and enhancements. Kawasaki made further styling changes and eventually removed the electrofusion coating that overheated cylinder heads and melted pistons. The firm replaced this with T-Treatment, which improved the general health and performance of the wheeler.

The Kawasaki 125 Dirt Bike is a rock-solid off-road vehicle. Sure, some model years had their dips while others were categorized as in-betweens. But overall, it was better than most of its competition.

Thanks to this little trailblazer, high-performance wheelers like the undisputed Kawasaki KX 500 came into existence. More importantly, both beginner and experienced riders can now enjoy a highly capable and spirited all-rounder – whether on the streets or in the outdoors.

Kris Peter

Adventure seeker and off-road enthusiast. I love the thrill of going off-road and taking on the elements.

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