1986 YZ 490 Manual

The 1986 YZ 490 is a high-performance motocross motorcycle featuring a powerful 490cc two-stroke engine, advanced suspension system, lightweight frame design, and competition-ready components. This manual covers essential information for proper operation, maintenance, troubleshooting, and specifications of this iconic dirt bike. Below are key sections for safety, features, operation, maintenance, and technical specifications.

Features at a Glance

Key components: 490cc two-stroke engine, Monoshock rear suspension, front and rear drum brakes, aluminum swingarm, competition tires.

Feature	Description
Engine Type	490cc air-cooled two-stroke single
Transmission	5-speed constant mesh
Suspension Front	Air-adjustable telescopic fork
Suspension Rear	Fully adjustable Monoshock
Brakes Front/Rear	Drum brakes
Frame	Steel semi-double cradle
Weight	Approximately 230 lbs (104 kg)
Fuel Capacity	2.6 gallons (10 liters)
Seat Height	36.2 inches (920 mm)
Ground Clearance	12.6 inches (320 mm)

Safety Information

Always wear proper protective gear and follow safe riding practices.

1. Always wear DOT-approved helmet, eye protection, gloves, and protective clothing.
2. Inspect motorcycle before each ride: tires, brakes, controls, lights.
3. Ride within your skill limits and be aware of terrain conditions.
4. Never operate under the influence of alcohol or drugs.

WARNING! This is a high-performance competition motorcycle. Proper training and experience are required for safe operation.

Operation Instructions

Proper starting and riding procedures for optimal performance.

1. Starting procedure: Turn fuel on, choke for cold starts, kick start with decompression lever.
2. Warm-up: Allow engine to reach operating temperature before aggressive riding.
3. Shifting: Use clutch for smooth gear changes; match engine RPM to road speed.
4. Braking: Apply both front and rear brakes progressively; avoid locking wheels.

CAUTION! Always check throttle operation and brake function before riding.

Specifications

• Engine: 490cc two-stroke single cylinder
• Bore x Stroke: 86.0 x 85.0 mm
• Compression Ratio: 7.5:1
• Carburetor: Mikuni VM38SS
• Ignition: CDI electronic ignition
• Transmission: 5-speed constant mesh
• Final Drive: #520 chain
• Suspension Travel Front: 11.8 inches (300 mm)
• Suspension Travel Rear: 12.2 inches (310 mm)
• Tire Size Front: 3.00-21
• Tire Size Rear: 5.10-18

Controls and Components

Familiarize yourself with all controls before operation.

Right Handlebar: Throttle, front brake lever, engine kill switch. Left Handlebar: Clutch lever, decompression lever, horn button. Foot Controls: Gear shift lever (left), rear brake pedal (right). Instrumentation: Speedometer, tachometer, indicator lights.

Fuel System: Petcock with ON, RESERVE, OFF positions. Choke lever for cold starting. Air filter access under seat.

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

1. After each ride: Clean air filter, check tire pressure, inspect for damage.
2. Every 10 hours: Change transmission oil, check chain tension and lubrication.
3. Every 20 hours: Clean spark plug, check brake pad wear, inspect suspension.
4. Every 50 hours: Top end inspection, wheel bearing service, cable lubrication.

Tip: Keep detailed maintenance records for reference.

Engine Service

Two-stroke engine maintenance and troubleshooting procedures.

1. Spark Plug: NGK B9ES, gap 0.024-0.028 inches.
2. Fuel Mix: 32:1 ratio (4 ounces oil per gallon) with high-quality two-stroke oil.
3. Compression Test: Should read 150-170 psi for healthy engine.
4. Carburetor Adjustment: Pilot jet 50, main jet 420, needle clip position 3.
5. Reed Valve: Inspect for cracks or damage during top end service.
6. Exhaust System: Regular cleaning of expansion chamber and silencer.
7. Crank Seals: Replace if engine runs lean or has starting difficulties.

WARNING! Engine components get extremely hot during operation. Allow proper cooling before servicing.

Suspension and Chassis

Adjustment and maintenance of suspension components and frame.

Front Fork: Air pressure adjustment for different riding conditions. Fork oil: 10W, 435ml per leg. Rear Shock: Spring preload adjustment, compression and rebound damping settings. Steering Head: Regular bearing inspection and adjustment. Swingarm: Pivot bolt lubrication every 20 hours. Wheel Alignment: Ensure proper alignment for straight tracking.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Hard starting	Fouled plug, stale fuel	Replace spark plug; use fresh fuel mix; check compression
Poor performance	Clogged air filter, jetting	Clean air filter; adjust carburetor; check reed valve
Transmission issues	Low oil, worn clutch	Check oil level; inspect clutch plates; adjust cable
Brake problems	Worn pads, contamination	Replace brake pads; clean drum surfaces; adjust cables
Suspension bottoming	Low air pressure, worn oil	Adjust air pressure; change fork oil; check spring preload

Professional Service: Complex repairs should be performed by qualified technicians.

Parts and Accessories

Genuine Yamaha parts ensure proper fit and performance.

Common replacement parts: Piston kits, gasket sets, brake shoes, chains, sprockets, cables. Performance upgrades: Aftermarket exhaust systems, reed valves, carburetors. Availability: Contact authorized Yamaha dealers for genuine parts. Aftermarket support: Various manufacturers produce compatible components.

Note: Use only recommended parts to maintain performance and safety standards.