1986 Honda CR250 Service Manual

The 1986 Honda CR250 is a high-performance two-stroke motocross motorcycle featuring a 249cc liquid-cooled engine, Pro-Link rear suspension, and advanced chassis design. This service manual covers complete maintenance procedures, specifications, troubleshooting, and repair instructions for the entire motorcycle. Below are key sections for safety, specifications, maintenance procedures, engine service, chassis repair, and troubleshooting.

1. General Information 2. Specifications 3. Periodic Maintenance 4. Engine Service 5. Fuel System 6. Chassis & Suspension 7. Electrical System 8. Brake System 9. Troubleshooting 10. Wiring Diagrams

General Information

Key components: 249cc two-stroke engine, Pro-Link rear suspension, front and rear disc brakes, aluminum frame, Mikuni carburetor.

Component	Description
Engine Type	249cc liquid-cooled single-cylinder two-stroke
Bore x Stroke	67.0mm x 70.8mm
Compression Ratio	8.4:1
Carburetor	Mikuni VM36SS
Ignition System	CDI electronic ignition
Transmission	5-speed constant mesh
Final Drive	#520 chain
Suspension Front	Air-adjustable telescopic fork
Suspension Rear	Pro-Link single shock
Brakes Front/Rear	Single disc

Specifications

Overall Length: 2,185mm (86.0 in)
Overall Width: 825mm (32.5 in)
Overall Height: 1,220mm (48.0 in)
Wheelbase: 1,485mm (58.5 in)
Ground Clearance: 345mm (13.6 in)
Seat Height: 955mm (37.6 in)
Dry Weight: 98kg (216 lbs)
Fuel Capacity: 8.5 liters (2.2 US gal)
Oil Capacity: 750ml (0.79 US qt)
Fuel/Oil Ratio: 20:1 (break-in), 32:1 (normal)

Periodic Maintenance

Regular maintenance schedule for optimal performance and longevity.

Before each ride: Check fuel level, tire pressure, chain tension, brake operation.
Every 6 hours: Clean air filter, check spark plug, inspect brakes.
Every 12 hours: Change transmission oil, check wheel bearings, inspect suspension.
Every 24 hours: Top end inspection, carburetor adjustment, fork oil change.
Every 48 hours: Complete engine rebuild, chassis bearing replacement.

WARNING! Always use proper safety equipment and follow torque specifications. Engine components get extremely hot during operation.

Engine Service

Complete engine disassembly, inspection, and reassembly procedures.

Cylinder Head Removal: Drain coolant, remove spark plug, disconnect hoses, remove head bolts.
Cylinder Removal: Remove exhaust pipe, intake manifold, cylinder base nuts.
Piston Removal: Remove circlips, wrist pin, piston.
Crankcase Splitting: Remove engine from frame, separate case halves.
Crankshaft Service: Inspect bearings, seals, connecting rod play.
Transmission Service: Gear inspection, shift mechanism adjustment.
Reassembly: Reverse procedure with new gaskets and seals.

Torque Specifications: Cylinder head 22 ft-lb, cylinder base 18 ft-lb, clutch spring 7 ft-lb.

Fuel System

Mikuni VM36SS carburetor service and adjustment procedures.

Carburetor Removal: Drain fuel, disconnect throttle cable, remove intake clamps.
Disassembly: Remove float bowl, float, needle valve, jets.
Cleaning: Use carburetor cleaner and compressed air.
Jet Specifications: Main jet #420, pilot jet #40, needle clip 2nd position.
Float Height: 16.5mm adjustment.
Air Screw: 1.5 turns out from lightly seated.
Reinstallation: Reverse procedure with new gaskets.

Tip: Always use fresh pre-mixed fuel and clean air filter for optimal performance.

Chassis & Suspension

Frame, suspension, and steering maintenance procedures.

Front Fork Service: Remove wheel, loosen triple clamps, drain oil.
Fork Oil Capacity: 415ml per leg (10wt fork oil).
Rear Shock Service: Remove shock, disassemble, replace seals.
Pro-Link Linkage: Grease bearings every 12 hours.
Steering Head: Adjust bearing preload, replace if worn.
Swingarm Pivot: Remove, inspect bearings, repack with grease.
Wheel Bearings: Remove seals, inspect, replace if necessary.

CAUTION! Use proper tools for suspension disassembly. Springs are under high tension.

Electrical System

CDI ignition, lighting, and charging system service.

Component	Specification
Spark Plug	NGK BR9ES (gap 0.6-0.7mm)
Ignition Timing	1.8mm BTDC (fixed)
Resistance Values	Primary 0.1-0.3Ω, Secondary 4.5-6.5kΩ
Battery	Not applicable (magneto only)
Lighting Coil	0.1-0.3Ω (yellow to ground)
Source Coil	200-300Ω (black/red to ground)
Pulse Generator	20-30Ω (blue/yellow to white/red)

Brake System

Front and rear disc brake service and maintenance.

Brake Pad Replacement: Remove caliper, replace pads, check rotor.
Brake Fluid Change: Use DOT 4 fluid, bleed system.
Caliper Service: Remove, disassemble, replace seals.
Master Cylinder: Disassemble, inspect bore, replace seals.
Brake Disc: Measure thickness, check for warpage.
Brake Line Inspection: Check for cracks, replace if damaged.

WARNING! Brake fluid is corrosive. Avoid contact with painted surfaces.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Hard starting	Fouled plug, stale fuel, compression	Replace spark plug, use fresh fuel, check compression
Poor performance	Clogged jets, air leak, exhaust restriction	Clean carburetor, check seals, clean exhaust
Transmission issues	Bent shift fork, worn gears	Split cases, inspect transmission
Suspension bottoming	Low oil, worn springs	Change fork oil, replace springs
Brake fade	Contaminated pads, air in system	Replace pads, bleed brakes
Overheating	Low coolant, water pump failure	Check coolant level, inspect pump

Compression Test: Should be 150-180 psi. Below 120 psi indicates need for top end rebuild.

Wiring Diagrams

Complete electrical schematics for the 1986 Honda CR250.

CDI Ignition System Wiring
Lighting Circuit Diagram
Kill Switch Circuit
Ground Points Location
Connector Pinouts

Refer to original factory wiring diagrams for color codes and connector locations. All wiring uses standard Honda color coding: Black-ground, Red-power, Blue/Yellow-pulse generator, etc.