Historical Context:
The Yamaha XS400 series represented Yamaha's entry into the mid-weight segment of the motorcycle market, offering a blend of performance, reliability, and style that appealed to a broad range of riders.
Key Competitors:
Competed against models like the Kawasaki KZ400, Honda CB400 series, and Suzuki GS400 during its production run.
Model Variants:
This manual likely covers various sub-models within the XS400 line, potentially including standard, Special, and Custom variants, which may have minor differences in styling and some components.
Manual Value Proposition:
Empowers owners and technicians with dealership-level repair and maintenance knowledge, enabling cost savings and ensuring proper upkeep.
Engine Systems:
Engine overhaul, disassembly and assembly, tuning, lubrication system, cooling system (if applicable), engine internals (pistons, rings, crankshaft, camshafts), valve train.
Fuel System:
Carburetor(s) disassembly, cleaning, adjustment, and synchronization; fuel lines, fuel tank, fuel pump (if applicable).
Ignition System:
Ignition timing, spark plugs, ignition coils, CDI unit, wiring, charging system (stator, rectifier/regulator).
Transmission And Drivetrain:
Gearbox disassembly and assembly, clutch operation and adjustment, drive chain maintenance and adjustment, internal transmission components.
Electrical System:
Wiring diagrams, lighting (headlight, taillight, indicators), starter system, battery, switches, fuses, instrumentation.
Chassis And Suspension:
Front fork disassembly, servicing, and adjustment; rear shock absorber servicing or replacement; swingarm maintenance; wheel bearing service; steering head bearing service.
Brakes:
Front and rear brake system servicing (disc or drum), brake caliper overhaul, brake pad replacement, brake fluid bleeding, brake cable adjustment.
Bodywork And Trim:
Body panel removal and installation, seat, fenders, fuel tank mounting, minor cosmetic repairs.
Exhaust System:
Exhaust pipe and muffler removal/installation, gasket replacement.
Routine Maintenance:
Oil changes, filter replacement, spark plug replacement, chain lubrication and adjustment, brake adjustments, tire pressure checks, general inspections.
Troubleshooting:
Diagnostic procedures for common and uncommon issues, symptom-based troubleshooting guides.
Repair And Overhaul:
Detailed step-by-step instructions for component disassembly, repair, reassembly, and adjustment.
Tune Up Procedures:
Carburetor synchronization, ignition timing adjustment, valve clearance checks and adjustments.
Special Tool Identification:
Identification and use of specialized tools required for specific tasks and adjustments.
Depth Of Coverage:
Comprehensive, covering routine maintenance through complete engine and transmission rebuilds.
User Level Assumption:
Primarily targeted at mechanical technicians familiar with motorcycle service procedures, but accessible to skilled DIY enthusiasts.
Engine Type:
Air-cooled, four-stroke, parallel-twin
Displacement:
Approximately 392cc to 425cc (depending on specific sub-model and bore/stroke configurations)
Bore X Stroke:
Varies by specific model, e.g., 63.0 mm x 64.0 mm for some models.
Compression Ratio:
Typically around 9.0:1 to 9.5:1
Horsepower Output:
Approx. 27-36 HP (at the crankshaft), depending on year and tuning
Torque Output:
Approx. 23-30 lb-ft (at the crankshaft), depending on year and tuning
Carburetion:
Dual Mikuni VM or BS series carburetors (e.g., 34mm)
Fuel Type:
Unleaded gasoline (octane rating specified in manual)
Ignition System Type:
CDI (Capacitor Discharge Ignition)
Oil Type:
Yamaha recommends specific motorcycle-grade 4-stroke engine oil (e.g., SAE 20W-40 or 10W-40, depending on climate).
Oil Capacity:
Approx. 2.0 - 2.5 liters (with filter change), specific value in manual.
Safety Standards Compliance:
Adheres to contemporary motorcycle safety standards of its era. Manual emphasizes safe operating procedures.
Braking System:
Front: Disc brake. Rear: Disc or Drum brake (depending on model year/variant).
Frame Construction:
Steel cradle frame for rigidity and rider support.
Lighting Systems:
Includes headlight, taillight, and turn signals for visibility.
Oil Change Interval:
Recommended every 3,000-5,000 km (1,800-3,000 miles) or annually. Specific interval detailed in manual.
Valve Adjustment Interval:
Recommended every 6,000-10,000 km (3,700-6,000 miles) or as per manual schedule.
Chain Maintenance:
Lubrication and adjustment every 800-1,000 km (500-600 miles).
Brake Fluid:
DOT 3 or DOT 4 hydraulic brake fluid (refer to manual for exact type and specification).
Gear Oil:
Gearbox oil type and capacity specified in manual, often a hypoid gear oil or similar.
Carburetor Tuning:
Carburetors can be sensitive to wear and require regular synchronization and cleaning. Pilot jets can clog.
Electrical Connections:
Older wiring harnesses can develop corrosion or loose connections, leading to intermittent electrical issues.
Valve Clearance:
Valve clearances can tighten or loosen over time, requiring periodic adjustment to maintain optimal engine performance and longevity.
Cam Chain Tensioner:
Some models may have specific maintenance requirements for the cam chain tensioner to prevent noise or wear.
Spark Plug Type:
Typically NGK or Denso plugs, e.g., NGK B8ES or equivalent. Specific recommendation in manual.
Tire Sizes:
Front: e.g., 3.00-18 or 90/90-18. Rear: e.g., 3.50-18 or 110/90-18. Specific sizes in manual.
Tire Pressure:
Refer to manual for recommended pressures for front and rear tires, adjusted for load and riding conditions.
Torque Specifications:
Crucial fasteners (e.g., cylinder head bolts, crankcase bolts, wheel nuts) have specific torque values detailed in the manual, essential for proper assembly and preventing damage.
Yamaha Motorcycles:
Yamaha Motor Company has a long and storied history in motorcycle manufacturing, known for innovation, performance, and racing success across various categories.
Xs Series Significance:
The XS series, including the XS400, was a pivotal part of Yamaha's lineup, establishing its presence in the popular mid-size motorcycle segment.
Production Period:
Covered by this manual: 1977-1982. The XS400 platform continued in various forms for several years beyond.
