1988 YZ250 Manual

The 1988 Yamaha YZ250 is a high-performance motocross motorcycle featuring a liquid-cooled 249cc two-stroke engine, 43mm conventional forks, Monoshock rear suspension, and advanced racing components. This manual covers maintenance procedures, specifications, troubleshooting, and repair guidelines for optimal performance and longevity.

1. Specifications 2. Maintenance Schedule 3. Engine Service 4. Chassis & Suspension 5. Electrical System 6. Fuel System 7. Troubleshooting 8. Torque Specifications 9. Safety Precautions 10. Warranty Information

Specifications

Technical specifications for the 1988 YZ250 motocross motorcycle.

Component	Specification
Engine Type	Liquid-cooled, 2-stroke, single cylinder
Displacement	249cc
Bore x Stroke	67.0 x 70.8mm
Compression Ratio	8.6:1
Carburetor	Mikuni VM38SS
Ignition	CDI
Transmission	5-speed constant mesh
Front Suspension	43mm conventional telescopic forks
Rear Suspension	Monoshock with adjustable preload
Front Brake	Single disc
Rear Brake	Single disc
Dry Weight	102 kg (225 lbs)
Fuel Capacity	9.5 liters (2.5 gallons)

Maintenance Schedule

Regular maintenance intervals for optimal performance and reliability.

Before each ride: Check fuel level, tire pressure, chain tension, brake operation
Every 10 hours: Clean air filter, check spark plug, inspect brakes
Every 20 hours: Change transmission oil, check wheel bearings
Every 50 hours: Replace spark plug, inspect suspension components
Every 100 hours: Top end rebuild, inspect crankshaft

WARNING! Always perform maintenance in well-ventilated area. Use proper safety equipment.

Engine Service

Engine maintenance and repair procedures for the 249cc two-stroke motor.

Top end rebuild: Remove cylinder head, inspect piston and rings
Carburetor adjustment: Main jet 420, pilot jet 50, needle clip position 3
Ignition timing: Set to factory specification 1.8mm BTDC
Cooling system: Check radiator fluid level, inspect hoses for leaks
Exhaust system: Regular cleaning of expansion chamber and silencer

CAUTION! Engine components get extremely hot. Allow proper cooling before servicing.

Chassis & Suspension

Frame: Steel perimeter frame with aluminum swingarm
Front Forks: 43mm conventional, 300mm travel
Rear Suspension: Monoshock, 320mm wheel travel
Front Brake: Single 240mm disc, twin-piston caliper
Rear Brake: Single 220mm disc, single-piston caliper
Wheels: 21-inch front, 19-inch rear
Tires: Front 80/100-21, Rear 110/90-19

Electrical System

CDI ignition system with lighting coil. Battery not required for operation.

Components: CDI unit, ignition coil, spark plug (BR8ES), stator assembly, kill switch.

Testing procedures: Check spark plug gap (0.6-0.7mm), ignition coil resistance (primary 0.1-0.3Ω, secondary 4.7-7.2kΩ), stator output (20-30V AC at 1000 RPM).

Fuel System

Mikuni VM38SS carburetor with standard jetting specifications.

Fuel mixture: 32:1 ratio (premium unleaded with 2-stroke oil)
Float level: 16.5mm
Main jet: 420
Pilot jet: 50
Needle: 6F21-3 (clip position 3)
Air screw: 1.5 turns out

Tip: Always use fresh fuel and proper 2-stroke oil mixture.

Troubleshooting

Common issues and solutions for the 1988 YZ250.

Symptom	Possible Cause	Corrective Action
Hard starting	Fouled spark plug, stale fuel	Replace spark plug, drain old fuel
Poor performance	Clogged air filter, incorrect jetting	Clean air filter, check carburetor settings
Overheating	Lean mixture, low coolant	Check jetting, refill coolant
Transmission issues	Low oil level, worn gears	Check oil level, inspect transmission
Brake problems	Worn pads, air in lines	Replace pads, bleed brakes

Torque Specifications

Critical torque values for proper assembly and safety.

Component	Torque Value
Cylinder head nuts	24 Nm (17 ft-lbs)
Spark plug	25 Nm (18 ft-lbs)
Front axle nut	65 Nm (47 ft-lbs)
Rear axle nut	105 Nm (76 ft-lbs)
Sprocket nuts	45 Nm (33 ft-lbs)
Fork clamp bolts	23 Nm (17 ft-lbs)

Safety Precautions

Always wear proper safety gear including helmet, goggles, gloves, boots, and protective clothing. Never operate motorcycle under influence of drugs or alcohol. Follow all local laws and regulations.

WARNING! Motorcycles are inherently dangerous. Proper training and protective gear are essential.

Warranty Information

Original 1988 Yamaha YZ250 warranty has expired. For replacement parts and technical support, contact authorized Yamaha dealers. Genuine Yamaha parts ensure proper fit and performance.