1986 KX125 Service Manual

The 1986 KX125 is a high-performance motocross motorcycle featuring a liquid-cooled 125cc two-stroke engine, 6-speed transmission, front and rear disc brakes, Uni-Trak rear suspension system, and Kawasaki's renowned handling characteristics. This service manual provides comprehensive technical information for maintenance, repair, and troubleshooting procedures. Below are key sections covering specifications, maintenance schedules, engine service, chassis, electrical systems, and troubleshooting.

General Information

Key components: Liquid-cooled 125cc two-stroke engine, 6-speed transmission, front disc brake, rear disc brake, Uni-Trak rear suspension, aluminum swingarm.

Component	Description
Engine Type	Liquid-cooled, single-cylinder two-stroke
Displacement	124cc
Bore x Stroke	54.0 x 54.0mm
Compression Ratio	8.4:1
Carburetor	Mikuni VM32SS
Ignition	CDI electronic ignition
Transmission	6-speed constant mesh
Final Drive	520 chain
Front Suspension	Air-adjustable telescopic fork
Rear Suspension	Uni-Trak system with adjustable shock

Specifications

• Overall Length: 2,175mm
• Overall Width: 830mm
• Overall Height: 1,200mm
• Wheelbase: 1,470mm
• Ground Clearance: 345mm
• Seat Height: 940mm
• Dry Weight: 89kg
• Fuel Capacity: 8.5 liters
• Front Tire: 80/100-21
• Rear Tire: 100/90-19
• Front Brake: Single disc, 240mm
• Rear Brake: Single disc, 240mm

Maintenance

Regular maintenance ensures optimal performance and longevity.

1. Pre-ride inspection: Check tire pressure, chain tension, brake operation, fluid levels.
2. Engine oil: Change every 15 hours or 500km (use recommended 2-stroke oil).
3. Air filter: Clean every 10 hours or 300km (use foam filter oil).
4. Spark plug: Replace every 30 hours or 1,000km (NGK BR9ES).
5. Chain adjustment: Maintain 25-35mm free play.
6. Brake pads: Inspect every 20 hours; replace if worn below 1mm.

WARNING! Always work on cool engine. Use proper safety equipment.

Engine

Complete engine service procedures and specifications.

1. Cylinder and piston: Inspect for wear; standard bore 54.000-54.015mm.
2. Crankshaft: Check runout (max 0.03mm); connecting rod side clearance 0.35-0.65mm.
3. Reed valve: Inspect for damage or wear; replace if gaps exceed 0.5mm.
4. Cylinder head: Check for warpage (max 0.03mm).
5. Cooling system: Check radiator for leaks; coolant capacity 850ml.
6. Exhaust system: Regular cleaning of expansion chamber and silencer.

CAUTION! Use torque wrench for critical fasteners.

Fuel System

Mikuni VM32SS carburetor service and adjustment.

1. Carburetor settings: Main jet #320, pilot jet #40, needle clip 3rd position.
2. Float level: 16.5mm ± 1.0mm
3. Throttle cable: Check for smooth operation; lubricate regularly.
4. Fuel filter: Clean every 50 hours.
5. Fuel mixture: 32:1 ratio (premium unleaded with 2-stroke oil).

Tip: Adjust jetting for altitude and temperature changes.

Chassis

Frame, swingarm, and wheel service procedures.

1. Frame inspection: Check for cracks or damage, especially around steering head and swingarm pivot.
2. Swingarm: Check bearing play; lubricate every 30 hours.
3. Wheel bearings: Inspect for smooth rotation; replace if rough or noisy.
4. Spokes: Check tension regularly; torque to 4 N·m.
5. Steering head bearings: Adjust for zero play; lubricate every 50 hours.

WARNING! Always support motorcycle securely when working on chassis.

Electrical System

CDI ignition, lighting, and charging system service.

1. Spark plug: NGK BR9ES, gap 0.6-0.7mm
2. Ignition coil resistance: Primary 0.1-0.3Ω, Secondary 4.5-6.5kΩ
3. Stator coil resistance: 180-220Ω
4. Battery: 12V 2.5Ah (if equipped with lighting kit)
5. Bulbs: Headlight 35W/35W, Brake light 21W, Turn signals 10W

CAUTION! Disconnect battery before electrical work.

Transmission

6-speed gearbox and clutch service procedures.

1. Transmission oil: Capacity 750ml, change every 30 hours
2. Clutch: Check cable free play 2-3mm at lever
3. Clutch plates: Standard thickness 2.92-3.08mm
4. Gear shifting: Adjust shift mechanism if not engaging properly
5. Drive chain: 520 type, 112 links, maintain 25-35mm free play

Tip: Use recommended transmission oil for smooth shifting.

Suspension

Front forks and rear Uni-Trak system service.

1. Front fork oil: Capacity 355ml per leg, viscosity 10W
2. Fork springs: Free length 483mm (replace if below 475mm)
3. Rear shock: Nitrogen pressure 1.0-1.2 MPa
4. Suspension settings: Adjust compression and rebound for track conditions
5. Bushings and seals: Replace if leaking or worn

WARNING! Release air pressure before disassembling forks.

Brakes

Front and rear disc brake service and maintenance.

1. Brake pads: Replace if thickness below 1.0mm
2. Brake fluid: DOT 4, change every 2 years
3. Disc thickness: Standard 4.0mm, minimum 3.5mm
4. Brake calipers: Clean and lubricate sliding pins every 30 hours
5. Master cylinders: Check for leaks and proper operation

CAUTION! Avoid getting brake fluid on painted surfaces.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Hard starting	Fouled plug, stale fuel	Replace spark plug; drain old fuel; check compression
Poor performance	Clogged air filter, jetting	Clean air filter; check carburetor settings; inspect reeds
Transmission noise	Low oil, worn gears	Check oil level; inspect transmission components
Brake fade	Contaminated pads, old fluid	Replace pads and fluid; clean discs
Overheating	Low coolant, lean mixture	Check coolant level; inspect jetting; clean radiator

Technical Support: Contact Kawasaki authorized service center for complex issues.

Parts: Use genuine Kawasaki parts for optimal performance and reliability.