1986 Yamaha YZ490 Owners Manual

The 1986 Yamaha YZ490 is a legendary motocross bike featuring a powerful 490cc two-stroke engine, advanced suspension system, and competition-ready chassis. This manual provides comprehensive information for proper operation, maintenance, and troubleshooting of your YZ490. Below are key sections covering safety, specifications, operation, maintenance, and technical details.

1. Features at a Glance 2. Safety Information 3. Specifications 4. Controls and Instruments 5. Operation Instructions 6. Maintenance Schedule 7. Engine Maintenance 8. Chassis Maintenance 9. Troubleshooting 10. Storage Instructions 11. Warranty Information

Features at a Glance

Key components: 490cc two-stroke engine, Monoshock rear suspension, front telescopic forks, aluminum swingarm, competition frame.

Feature	Description
Engine Type	490cc air-cooled two-stroke single
Bore x Stroke	86.0 x 85.0 mm
Compression Ratio	7.5:1
Carburetor	Mikuni VM38SS
Transmission	5-speed constant mesh
Suspension Front	Telescopic forks, 11.8 inches travel
Suspension Rear	Monoshock, 12.2 inches travel
Brakes Front	Single disc
Brakes Rear	Drum brake
Fuel Capacity	2.6 gallons

Safety Information

Always wear proper protective gear and follow safety procedures.

Always wear DOT-approved helmet, eye protection, gloves, and protective clothing.
Inspect motorcycle before each ride for proper operation.
Never operate under influence of alcohol or drugs.
Follow all local laws and regulations.
Keep hands and feet away from moving parts.

WARNING! This is a high-performance competition motorcycle. Operation requires skill and experience. Always ride within your limits.

Specifications

Engine: 490cc two-stroke single cylinder
Power Output: Approximately 45 horsepower
Ignition System: CDI electronic ignition
Starting System: Kick start
Lubrication System: Premix (32:1 fuel/oil ratio)
Frame: Steel semi-double cradle
Wheelbase: 58.7 inches
Ground Clearance: 13.0 inches
Seat Height: 37.4 inches
Dry Weight: 238 pounds

Controls and Instruments

Familiarize yourself with all controls before operation.

Right Handlebar: Throttle control, front brake lever, engine kill switch.

Left Handlebar: Clutch lever, choke knob, horn button, light switch.

Instrument Panel: Speedometer, odometer, neutral indicator light, high beam indicator.

Foot Controls: Gear shift lever (left), rear brake pedal (right), kick starter.

Operation Instructions

Proper starting and riding procedures for optimal performance.

Fuel Mix: Use premium unleaded gasoline with high-quality two-stroke oil at 32:1 ratio.
Starting: Turn fuel valve ON, pull choke, kick start firmly.
Warm-up: Allow engine to warm for 2-3 minutes before riding.
Shifting: Use clutch for smooth gear changes; avoid lugging engine.
Braking: Use both brakes together for controlled stopping.

CAUTION! Always allow engine to warm up properly. Cold engine operation can cause damage.

Maintenance Schedule

Regular maintenance ensures reliability and performance.

Item	Every Ride	Every 10 Hours	Every 20 Hours
Engine Oil	Check level	Change	-
Air Filter	Visual check	Clean	Replace
Spark Plug	-	Check/clean	Replace
Chain	Check tension	Lubricate	Adjust
Brakes	Check operation	Inspect pads	-

Engine Maintenance

Critical engine service procedures.

Spark Plug: NGK B9ES, gap 0.024-0.028 inches.
Air Filter: Clean with filter oil and re-oil regularly.
Carburetor: Adjust idle speed 1200-1400 RPM.
Cylinder: Check compression regularly (120-150 psi).
Exhaust: Clean power valve system every 20 hours.

Tip: Use only Yamaha recommended parts and lubricants.

Chassis Maintenance

Suspension, brakes, and frame maintenance.

Fork Oil: Change every 40 hours of operation.
Rear Shock: Check nitrogen pressure every 30 hours.
Chain: Maintain 1.5-2.0 inches free play.
Wheel Bearings: Repack with grease every 50 hours.
Spokes: Check and tighten regularly.

WARNING! Always support motorcycle securely when performing maintenance.

Troubleshooting

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

Service: Contact authorized Yamaha dealer for major repairs.

Storage Instructions

Proper storage procedures for extended periods.

Drain fuel from carburetor and tank.
Remove spark plug and add teaspoon of oil to cylinder.
Clean and lubricate entire motorcycle.
Store in dry, covered area.
Inflate tires to maximum pressure.

CAUTION! Always use fuel stabilizer if storing with fuel in tank.

Warranty Information

1986 Yamaha YZ490 limited warranty coverage. Original warranty period has expired. For technical support and parts, contact authorized Yamaha dealers. Yamaha Motor Corporation, U.S.A. Customer Relations: 1-800-962-7926. Always use genuine Yamaha parts for optimal performance and reliability.