The Suzuki GS and GSX Twins represent a significant era in Japanese motorcycle engineering, produced between 1979 and 1985. These models, available in 250cc, 400cc, and 450cc engine variants, were designed with an emphasis on DOHC engine technology and sporty styling, positioning them as performance-oriented machines in a competitive market. Known for their robust construction and advanced features for the time, such as sophisticated suspension systems, these motorcycles have become classics, appreciated for their reliability and engaging riding experience. This comprehensive factory service manual provides essential guidance for the maintenance, repair, and restoration of your Suzuki GS/GSX Twins. Covering all models from 1979 through 1985, this over 500-page English-language guide details every major system, including the engine, fuel, ignition, transmission, drivetrain, suspension, brakes, and electrical systems. It offers step-by-step repair procedures, routine maintenance schedules, troubleshooting diagnostics, and technical specifications, making it an indispensable resource for owners and technicians seeking to preserve the performance and longevity of these iconic motorcycles. 🏷️ Basic Information Identification Make: Suzuki Model: GS / GSX Twins Engine Variants: 250cc, 400cc, 450cc Codes Product Code: Suzuki_GS_GSX_250_400_450_Twins_1979_1985_Service_Manual_PDF_Download 👋 Introduction Market Position Segment: Performance-oriented Japanese motorcycles of the early 1980s, competing in the lightweight to mid-weight sportbike and standard categories. Competitive Analysis Competitors: Yamaha XS/XJ series, Honda CB/CB-F series, Kawasaki KZ/GPz series of similar displacements. Key Features Design Philosophy: Emphasis on DOHC parallel-twin or inline-four engines, advanced suspension for the era, and sporty styling. Manual Value Proposition: Essential guide for owners and technicians to maintain, repair, and restore these classic Suzuki twins, ensuring longevity and optimal performance. 📋 Manual Details Coverage Areas Years Covered: 1979, 1980, 1981, 1982, 1983, 1984, 1985 Models Covered: Suzuki GS/GSX 250cc Twins, Suzuki GS/GSX 400cc Twins, Suzuki GS/GSX 450cc Twins Page Count Estimated Page Count: 500+ Manual Type Type: Factory Service Manual / Repair Manual Language Language: English Format Format: PDF Download 📖 Manual Coverage Systems Covered Engine: Engine removal, disassembly, inspection, repair, reassembly, tuning, lubrication, cooling system, oil pressure. Fuel System: Carburetor identification, adjustment, overhaul, fuel pump, fuel lines, fuel tank. Ignition System: CDI unit, ignition coils, spark plugs, timing, troubleshooting. Transmission: Gearbox removal, disassembly, inspection, repair, clutch operation, shift mechanism. Drivetrain: Final drive, chain maintenance, sprockets, swingarm, rear suspension linkage. Suspension: Front forks (telescopic), rear shock absorbers, spring rates, oil levels, seals. Brakes: Front and rear brake systems, hydraulic lines, calipers, master cylinders, brake fluid specifications, bleeding procedures, disc and pad wear. Electrical System: Wiring diagrams, battery, alternator, starter motor, lighting, horn, switches, fuses, relays, troubleshooting electrical faults. Frame And Bodywork: Frame inspection, fork gaiters, fuel tank, seat, fenders, side covers, instrument panel. Procedures Included Maintenance: Regular service checks, oil changes, filter replacements, spark plug replacement, chain adjustment, lubrication points. Troubleshooting: Diagnostic guides for common engine, electrical, and mechanical problems, symptom-based fault finding. Repair: Detailed step-by-step instructions for component removal, repair, and reinstallation for all major systems. Disassembly Reassembly: Complete breakdown and reassembly procedures for engine, transmission, suspension, and other key components. Adjustments: Carburetor synchronization, valve clearance adjustment, brake lever travel, clutch cable play. Technical Depth Depth: Comprehensive rebuild and diagnostic information suitable for professional mechanics and experienced DIY enthusiasts. 📊 Manual Specifications File Format Quality: High-resolution scans, searchable text (OCR). Print Quality Printability: Printable pages for workshop use. Binding Type Binding: N/A (Digital PDF) Paper Type Paper: N/A (Digital PDF) ⚙️ Engine Specifications Primary Engine Configuration: DOHC, Parallel-Twin (250, 450cc), DOHC, Inline-Four (400cc - though some 400 twins existed) Bore Stroke 250: Varies by specific model, typically around 50mm x 31.8mm (GS250) Bore Stroke 400: Varies by specific model, e.g., 52mm x 47mm (GS400 Inline-Four) Bore Stroke 450: Varies by specific model, typically around 65mm x 65mm (GS450 Twin) Cooling System: Air-cooled Performance Horsepower 250: Approx. 26-30 HP (varies by model and tuning) Horsepower 400: Approx. 35-45 HP (varies by model and tuning) Horsepower 450: Approx. 35-40 HP (varies by model and tuning) Fuel System Carburetor Type: Mikuni VM or BS series, Keihin CV (Constant Velocity) carburetors, typically dual carbs. Fuel Tank Capacity: Typically 10-14 liters (2.6-3.7 US gallons) depending on model. 🔧 Transmission Standard Type: 6-speed constant mesh manual transmission. Optional Type: N/A (Manual transmission was standard) Features Clutch: Wet, multi-plate, cable-actuated clutch. Final Drive: O-ring sealed chain drive. 📐 Dimensions Exterior Wheelbase: Varies by model, typically around 1380-1440 mm (54.3-56.7 inches). Weights Dry Weight: Varies by model, typically 150-180 kg (330-397 lbs). 🛡️ Safety Features Ratings Crash Test Data: N/A (Motorcycle specific safety ratings from this era are not directly comparable to automotive standards). Active Features Braking System: Front disc brake(s) and rear drum or disc brake, depending on model and year. Linked braking systems were not common. Passive Features Lighting: Halogen headlight, taillight, brake light, turn signals. 💡 Technology Features Infotainment Features: Basic analog instrumentation (speedometer, tachometer, odometer, fuel gauge on some models), no electronic infotainment systems. Driver...