Positioning:
High-performance motocross and desert racing machine for experienced riders.
Competitors:
Competed against other large-bore 2-stroke motocross bikes of the era, such as Honda CR500, Suzuki RM465/500, and Kawasaki KX420/500.
Engine Type:
Powerful air-cooled 2-stroke single-cylinder engine.
Suspension System:
Yamaha's revolutionary Monocross rear suspension system for improved handling and comfort.
Handling Characteristics:
Known for brute power and strong low-end torque, suited for desert racing and rough terrain.
Primary Coverage:
Service, Repair, Workshop
Secondary Coverage:
Maintenance, Troubleshooting, Diagnostics, Specifications, Diagrams
Estimated Page Count:
Approx. 300-400 pages (typical for this era's comprehensive manuals)
Manual Type:
Factory Service Manual (FSM)
Format:
Downloadable Digital File (PDF)
Engine:
Complete disassembly, assembly, tuning, lubrication, cooling system, carburetion, ignition system, exhaust system
Transmission:
Clutch operation, gearbox disassembly, assembly, lubrication, shift mechanism
Chassis And Suspension:
Front fork (telescopic), rear suspension (monocross), swingarm, bearings, linkages, lubrication
Brakes:
Front and rear brake systems (likely drum, potentially early disc development), hydraulic lines, calipers, master cylinders, brake pads/shoes, bleeding procedures
Electrical System:
Ignition system (CDI), lighting system (if applicable), wiring diagrams, component testing, battery maintenance
Fuel System:
Fuel tank, petcock, fuel lines, carburetor tuning and rebuilding (likely Mikuni VM series)
Body And Frame:
Frame inspection, seat, fenders, fuel tank, side covers, handlebar, footpegs, mounting hardware
Basic Maintenance:
Oil changes, filter cleaning/replacement, chain adjustment, spark plug inspection/replacement, air filter service, brake adjustment
Engine Overhaul:
Piston and ring replacement, cylinder honing, crankshaft and connecting rod inspection/replacement, valve clearance adjustment (if applicable, though typically no valves in this 2-stroke), gasket replacement
Troubleshooting:
Diagnostic charts for common problems, symptom-based troubleshooting guides
Wheel And Tire:
Wheel bearing service, tire replacement, spoke tensioning, wheel balancing
Technical Adjustments:
Carburetor jetting, ignition timing, suspension sag and damping adjustments
Depth:
Comprehensive - covers routine maintenance, component-level repair, detailed diagnostic procedures, and complete engine/transmission rebuilds.
Engine Type:
2-Stroke, Reed Valve, Single Cylinder
Bore X Stroke:
85.0 mm x 86.0 mm
Cooling System:
Air-cooled
Intake Method:
Reed valve induction
Carburetor:
Mikuni VM38SS (38mm slide valve)
Horsepower Estimate:
Approx. 45-50 HP at the crankshaft (factory estimate)
Torque Estimate:
Significant torque, especially in the low to mid-range.
Fuel Type:
Unleaded gasoline with 2-stroke oil pre-mix
Fuel Ratio:
Typically 20:1 or 30:1 depending on oil quality and riding conditions.
Overall Length:
Approx. 2,165 mm (85.2 in)
Overall Width:
Approx. 830 mm (32.7 in)
Overall Height:
Approx. 1,245 mm (49.0 in)
Wheelbase:
Approx. 1,460 mm (57.5 in)
Ground Clearance:
Approx. 320 mm (12.6 in)
Seat Height:
Approx. 950 mm (37.4 in)
Dry Weight:
Approx. 115 kg (253.5 lbs)
Wet Weight Estimate:
Approx. 125 kg (275.6 lbs)
Fuel Capacity:
10.0 L (2.6 US gal)
Oil Capacity Transmission:
0.9 L (0.95 US qt)
Oil Change Engine:
Every 5-10 hours of riding, or as specified in the manual, depending on operating conditions.
Air Filter Cleaning:
Every 2-5 hours of riding, critical for 2-stroke engine longevity.
Spark Plug Inspection:
Every 5-10 hours of riding.
Chain Lubrication Adjustment:
After every ride or every few hours, and as needed.
Top End Rebuild Estimate:
50-100 hours of aggressive riding for piston and rings, potentially longer for cylinder.
Transmission Oil Type:
Yamalube 10W-30 API Service SE or SF, or equivalent SAE 10W-30 motorcycle gear oil.
2 Stroke Oil:
High-quality 2-stroke motorcycle oil meeting JASO FD or FC standards, or pre-mix specifically for racing 2-strokes.
Engine Vibration:
Characteristic of large-bore 2-strokes; can be mitigated with proper maintenance and occasional engine mount checks.
Carburetor Tuning:
Can be sensitive to altitude, temperature, and modifications. Requires careful adjustment and cleaning.
Suspension Maintenance:
Monocross linkage and fork seals can wear over time and require regular inspection and servicing to maintain performance.
Clutch Wear:
High-performance clutch can wear faster under aggressive use; proper adjustment and fluid are key.
Yamaha Legacy:
Yamaha has a long and storied history in motorcycle racing, particularly in motocross and off-road disciplines, with a reputation for innovation and performance.
Yz490 Lineage:
The YZ490 was the pinnacle of Yamaha's large-displacement 2-stroke motocross line in the early to mid-1980s, evolving from earlier 465cc and 400cc models. It was known for its raw power and was a favorite for desert racing.
1984 Updates:
The 1984 model featured refinements over the previous year, often including updated suspension settings, revised styling, and potential engine tuning improvements, but remained largely based on the YZ490 platform introduced in 1981.
Production Years:
The YZ490 was produced from approximately 1981 to 1988.
Manufacturing Location:
Japan
