1987 YZ490 Manual

The 1987 Yamaha YZ490 is a high-performance motocross motorcycle featuring a 490cc two-stroke engine, liquid cooling system, front and rear suspension with adjustable damping, front disc brake, rear drum brake, aluminum frame, and competition-focused design. Below are key sections for safety, features, maintenance, operation, and troubleshooting.

Features at a Glance

Key components: 490cc two-stroke engine, Liquid cooling system, Front disc brake, Rear drum brake, Adjustable suspension, Aluminum frame, Competition tires.

Feature	Description
Engine	490cc two-stroke single cylinder
Cooling System	Liquid cooled with radiator
Front Brake	Hydraulic disc brake
Rear Brake	Mechanical drum brake
Front Suspension	Telescopic forks with adjustable damping
Rear Suspension	Monoshock with adjustable preload
Frame	Aluminum perimeter frame
Fuel Tank	2.1 gallon capacity
Transmission	5-speed constant mesh
Ignition	CDI electronic ignition

Installation & Assembly

Unpack and inspect contents. Assemble on stable surface.

1. Install handlebars: Position and tighten clamp bolts to specification.
2. Mount front wheel: Install axle and tighten to proper torque.
3. Install controls: Attach throttle, clutch, and brake levers.
4. Add fluids: Fill with recommended oil and coolant.

WARNING! Motorcycle is heavy; use proper lifting techniques. Ensure all fasteners are properly torqued.

First-Time Setup

Complete assembly; perform pre-ride inspection.

1. Check tire pressure: Front 12-15 psi, Rear 10-12 psi.
2. Adjust suspension: Set sag and damping for rider weight.
3. Set controls: Adjust lever positions for comfort.
4. Fuel mixture: Prepare 32:1 gas/oil ratio.

CAUTION! Always wear proper safety gear. Test brakes before riding.

Specifications

• Engine Type: 490cc two-stroke single cylinder
• Bore x Stroke: 86.0 x 84.0 mm
• Compression Ratio: 8.5:1
• Fuel System: 38mm Mikuni carburetor
• Transmission: 5-speed constant mesh
• Final Drive: Chain
• Front Suspension: Telescopic forks, 11.8 inches travel
• Rear Suspension: Monoshock, 12.2 inches travel
• Front Brake: Single disc, 240mm
• Rear Brake: Drum, 180mm
• Dry Weight: 229 lbs (104 kg)

Controls and Settings

Main controls: Throttle, Clutch lever, Front brake lever, Rear brake pedal, Gear shift lever, Kill switch.

Adjustable features: Suspension preload and damping, Lever positions, Handlebar position, Chain tension.

Carburetor adjustments: Air screw, Idle speed, Main jet, Pilot jet, Needle position. Suspension: Compression damping, Rebound damping, Spring preload.

Maintenance Procedures

Regular maintenance ensures optimal performance and longevity.

1. Air filter: Clean every 10-15 hours of operation.
2. Chain: Lubricate and adjust tension regularly.
3. Spark plug: Check and clean every 20 hours.
4. Coolant: Check level before each ride.
5. Brakes: Inspect pads and fluid regularly.

Tip: Keep maintenance log for service intervals.

Operating Instructions

Proper operation techniques for optimal performance.

1. Starting procedure: Use choke when cold, kick start firmly.
2. Warm-up: Allow engine to reach operating temperature.
3. Shifting: Use clutch for smooth gear changes.
4. Braking: Use both brakes together for maximum stopping power.
5. Cornering: Weight outside peg, look through turn.

WARNING! Always wear helmet and protective gear. Ride within your skill level.

Performance Features

Competition-focused design elements for motocross performance.

Powerband: Strong mid-range to top-end power delivery. Suspension: Long travel for rough terrain absorption. Frame: Lightweight aluminum for precise handling. Ergonomics: Aggressive riding position for control.

Care & Cleaning

Clean after each ride to maintain appearance and function.

Use mild soap and water for plastics and frame. Avoid high-pressure spray on bearings and seals. Lubricate chain after cleaning. Check for loose fasteners during cleaning.

CAUTION! Do not use harsh chemicals that may damage components.

Regulatory Information

Designed for closed-course competition use only. Not legal for street use in most jurisdictions. Yamaha Motor Corporation - all rights reserved. For technical support, contact authorized Yamaha dealer.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Hard starting	Fouled plug, stale fuel	Replace spark plug; drain old fuel mixture.
Poor performance	Clogged air filter, jetting	Clean air filter; check carburetor settings.
Overheating	Low coolant, lean mixture	Check coolant level; adjust fuel mixture.
Brake fade	Contaminated pads, air in system	Replace pads; bleed brake system.
Suspension bottoming	Incorrect spring rate, low oil	Adjust preload; check oil level in forks.

Service: Contact authorized Yamaha dealer for major repairs.