1986 KX 125 Manual

The 1986 KX 125 is a high-performance motocross motorcycle featuring a liquid-cooled 124cc two-stroke engine, 6-speed transmission, Uni-Trak rear suspension system, front and rear disc brakes, and lightweight aluminum frame. This manual covers maintenance procedures, specifications, troubleshooting, and repair guidelines for optimal performance and longevity.

Specifications

Technical specifications for the 1986 KX 125 motocross motorcycle.

Component	Specification
Engine Type	Liquid-cooled, single-cylinder two-stroke
Displacement	124cc
Bore x Stroke	54.0 x 54.0 mm
Compression Ratio	8.5:1
Carburetor	Keihin PWK 34mm
Transmission	6-speed constant mesh
Final Drive	520 chain
Suspension Front	Air-adjustable telescopic fork
Suspension Rear	Uni-Trak system with adjustable shock
Brakes Front/Rear	Hydraulic disc
Dry Weight	88 kg (194 lbs)
Fuel Capacity	7.5 liters (2.0 gallons)

Maintenance Schedule

Regular maintenance intervals for optimal performance and safety.

1. Before each ride: Check tire pressure, brake function, chain tension
2. Every 10 hours: Clean air filter, check spark plug
3. Every 20 hours: Change transmission oil, inspect brakes
4. Every 50 hours: Top end inspection, suspension service
5. Every 100 hours: Complete engine overhaul inspection

WARNING! Always perform maintenance on clean, level surface with engine off and cool.

Engine Service

Engine maintenance and repair procedures.

1. Top end rebuild: Remove cylinder head, inspect piston and rings
2. Crankcase service: Check bearings and seals for wear
3. Cylinder inspection: Measure bore for wear and out-of-round
4. Cooling system: Check radiator, hoses, and coolant level
5. Exhaust system: Clean expansion chamber and silencer

CAUTION! Use proper torque specifications when reassembling engine components.

Transmission & Clutch

• Transmission Oil: Use 10W-40 motorcycle oil, 750ml capacity
• Clutch Adjustment: Free play at lever: 10-15mm
• Shift Mechanism: Inspect shift forks and drum for wear
• Chain Adjustment: 25-35mm free play at midpoint
• Sprockets: Replace when teeth become hooked or worn

Suspension System

Front fork and rear Uni-Trak suspension maintenance.

Front Forks: Air pressure 0-6 psi, oil level 135mm from top

Rear Shock: Spring preload adjustable, nitrogen charge 142 psi

Inspect seals for leaks, check bushings for wear, adjust damping to riding conditions. Lubricate linkage bearings every 20 hours.

Brake System

Hydraulic disc brake maintenance and service.

1. Front brake: Check pad thickness (minimum 1.0mm)
2. Rear brake: Inspect rotor for warping or scoring
3. Brake fluid: DOT 4, change annually or when discolored
4. Caliper service: Clean and lubricate sliding pins
5. Bleeding: Remove air from system when spongy feel occurs

Tip: Always use clean, fresh brake fluid and avoid contamination.

Electrical System

Supports CDI ignition, lighting coil (where equipped).

1. Spark plug: NGK BR9ES, gap 0.6-0.7mm
2. CDI unit: Check for spark if engine won't start
3. Stator: Resistance 0.1-1.0 ohms (lighting coil)
4. Kill switch: Test for continuity when pressed
5. Battery: 12V (on models with electric start)

WARNING! Disconnect spark plug cap when working on ignition system.

Carburetor Adjustment

Keihin PWK carburetor settings and tuning.

Setting	Standard	Adjustment Range
Main Jet	#158	#150-#165
Pilot Jet	#52	#48-#55
Needle Clip	3rd position	2nd-4th position
Air Screw	1.5 turns out	1-2 turns out
Float Height	16mm	15-17mm

Troubleshooting

Common issues and solutions for the 1986 KX 125.

Symptom	Possible Cause	Corrective Action
Hard starting	Fouled plug, stale fuel	Replace spark plug; drain old fuel
Poor performance	Clogged air filter, jetting	Clean air filter; adjust carburetor
Transmission noise	Low oil, worn gears	Check oil level; inspect gears
Overheating	Low coolant, lean jetting	Check coolant; richen mixture
Brake fade	Contaminated fluid, worn pads	Change fluid; replace brake pads

Reset: Return carburetor to standard settings if tuning issues occur.

Safety Precautions

Always wear proper safety gear: helmet, goggles, gloves, boots, protective clothing. Inspect motorcycle before each ride. Never operate under influence of drugs or alcohol.

CAUTION! High-performance motorcycle requires skill and experience to operate safely.

Parts & Accessories

Genuine Kawasaki parts recommended for optimal performance and reliability. Aftermarket options available for various components. Contact authorized Kawasaki dealer for parts availability and technical support.

Service: Consult authorized Kawasaki service center for major repairs.