🏷️ Basic Information

Make:

Yamaha

Model:

QT50 QT 50

Year:

1979

Product Type:

Full Service Repair Manual

👋 Introduction

Vehicle Segment:

Lightweight, entry-level scooter, popular for recreational use, short-distance commuting, and as a fun, economical personal transport.

Competitors:

Competed with other small-displacement scooters from brands like Honda (e.g., Spree), Tomos, and Vespa during its production era.

Ease Of Use:

Automatic transmission and simple controls made it very accessible to new riders.

Economy:

Known for excellent fuel efficiency and low running costs.

Durability:

Yamaha's reputation for building reliable and durable small engines.

📋 Manual Details

Overall Coverage:

Comprehensive repair, maintenance, rebuilding, refurbishing, and restoration for the Yamaha QT50 QT 50 (1979).

Estimated Page Count:

Refer to product listing for exact page count, typically 100-300 pages for this type of manual.

Type:

Service/Repair Manual

Language:

English

Format:

Likely PDF, though physical printed versions may also be available. Specify format based on actual product offering.

📖 Manual Coverage

Engine:

Detailed disassembly, assembly, inspection, and repair of the 2-stroke engine, including cylinder, piston, crankshaft, bearings, seals, and lubrication system.

Fuel System:

Carburetor (Mikuni VM series typically) adjustment, cleaning, overhaul, fuel lines, fuel tank, and petcock.

Ignition System:

Flywheel magneto ignition, spark plug selection and gap, ignition timing, and troubleshooting.

Transmission Drivetrain:

Automatic centrifugal clutch, transmission gearing, drive chain inspection and adjustment, and lubrication.

Brakes:

Front and rear drum brake systems, brake shoe replacement, cable adjustment, and inspection.

Suspension:

Front fork (telescopic) disassembly, service, oil levels, and rear shock absorber inspection.

Electrical System:

Lighting system (headlight, taillight, indicators), horn, wiring diagrams, battery maintenance (if applicable), and fuse replacement.

Chassis Frame:

Frame inspection, steering head bearing adjustment, and general chassis component checks.

Bodywork Cosmetics:

Fender removal and installation, seat removal, handlebar adjustment, and minor cosmetic repairs.

Scheduled Maintenance:

Recommended maintenance intervals for oil changes, filter replacements, spark plug checks, and lubrication points.

Troubleshooting:

Diagnostic charts and guides for identifying and resolving common operational problems and failures.

Engine Rebuild:

Step-by-step instructions for complete engine disassembly, part inspection, measuring tolerances, and reassembly.

Carburetor Rebuild:

Detailed procedures for cleaning, inspecting, and replacing jets, needles, floats, and seals in the carburetor.

Brake Adjustment Replacement:

Guidance on adjusting brake cables, replacing brake shoes, and inspecting brake drums.

Suspension Service:

Instructions for fork oil change, seal replacement, and proper suspension component reassembly.

Electrical Component Testing:

Methods for testing ignition coil, stator, and lighting circuits, often using a multimeter.

Lubrication Points:

Identification of all lubrication points and recommended lubricant types and quantities.

Depth Level:

Detailed, suitable for home mechanics to professional technicians. Covers everything from basic adjustments to complete engine overhauls.

Precision Measurements:

Includes critical torque specifications, piston ring gap, bearing clearances, and other precision measurements.

Diagnostic Charts:

Extensive troubleshooting charts that correlate symptoms with likely causes and corrective actions.

Diagrams Illustrations:

Likely includes exploded views of components, detailed assembly diagrams, and electrical schematics.

📊 Manual Specifications

Digital Format:

Typically PDF for searchability and easy access on digital devices.

Quality:

Assumed to be of good quality, featuring clear text and legible diagrams. If physical, it would be professional printing.

Physical Binding:

If physical, typically comb-bound or perfect-bound for durability in a workshop environment.

Physical Paper:

If physical, often printed on durable, coated paper to resist grease and dirt.

⚙️ Engine Specifications

Engine Type:

2-stroke, air-cooled, single-cylinder

Displacement:

49cc (2.99 cu. in.)

Bore X Stroke:

37.0mm x 43.0mm (1.46 in. x 1.69 in.)

Compression Ratio:

Approximately 6.0:1

Power Output:

Around 3.0 - 3.5 PS (2.2 - 2.6 kW) at approx. 6000-6500 rpm (exact figures may vary by region/tuning)

Torque:

Low, but sufficient for its intended purpose. Specific figures not commonly advertised for this class.

Carburetor Model:

Typically Mikuni VM12 or similar small-bore carburetor.

Fuel Type:

Unleaded gasoline (minimum 87 octane recommended)

Oil Mixing:

2-stroke oil mixed with fuel at a 50:1 ratio (check manual for precise recommendation) or via Autolube system if equipped.

Fuel Capacity:

Approximately 3.5 - 4.0 liters (0.9 - 1.1 US gallons)

🔧 Transmission

Type:

Automatic centrifugal clutch with V-belt drive (CVT type system).

Gearbox:

No traditional gearbox; automatic operation.

Drive Mechanism:

Shaft drive or chain drive (confirm specific model configuration, chain drive is common for this era).

📐 Dimensions

Length:

Approx. 1600-1700 mm (63-67 inches)

Width:

Approx. 650-700 mm (25.6-27.6 inches)

Height:

Approx. 1000-1050 mm (39.4-41.3 inches)

Wheelbase:

Approx. 1100-1150 mm (43.3-45.3 inches)

Dry Weight:

Approx. 60-65 kg (132-143 lbs)

Gross Vehicle Weight Rating:

Not typically specified, but rider + cargo capacity is limited.

Front Tire Size:

Typically 2.50-10 or similar.

Rear Tire Size:

Typically 2.50-10 or similar.

Wheel Type:

Spoked wheels with tube-type tires.

🛡️ Safety Features

Crash Safety:

Not applicable in the same way as automobiles. Focus is on operational safety.

Braking System:

Drum brakes front and rear, designed for low-speed operation.

Lighting:

Headlight, taillight, brake light, and turn signals for visibility and communication.

Frame Integrity:

Steel frame construction for structural integrity.

Leg Shielding:

Plastic body panels offer minimal rider protection from elements.

💡 Technology Features

Features:

None. This is a basic, early 1980s scooter design.

Features:

None. Relies solely on rider input and basic mechanical systems.

Features:

None. Purely mechanical operation.

🔧 Maintenance

Oil Change Frequency:

Refer to manual, but typically every 1000-2000 km or annually for gearbox oil. Fuel/oil mix requires no specific interval beyond refueling.

Spark Plug Check:

Every 1000-2000 km or annually. Replacement as needed.

Air Filter Cleaning:

Regular inspection and cleaning, typically every 1000-2000 km, replacement as needed.

Brake Adjustment:

As needed, or every 1000-2000 km. Check for lever free play.

Drive Chain Lubrication:

Every 500-1000 km, depending on conditions. Check tension as well.

Transmission Oil:

Yamaha recommends specific gear oil for the transmission. Likely SAE 80W or SAE 10W-30 API GL-4 for small transmissions. Refer to manual for exact specification (e.g., Yamaha Hi-Performance Gear Oil).

Fork Oil:

Standard motorcycle fork oil, typically SAE 5W or 10W. Manual will specify weight and quantity per fork leg.

2 Stroke Oil:

High-quality 2-stroke motorcycle oil, suitable for air-cooled engines. Mix ratio of 50:1 is common.

Carburetor Clogging:

Common with older carbureted engines, especially if fuel sits for extended periods. Gumming of jets and passages.

Aging Rubber Components:

Fuel lines, intake boots, and brake cables can degrade over time, leading to leaks or performance issues.

Electrical Corrosion:

Connectors and wiring can corrode, leading to intermittent lights or ignition problems.

Worn Clutch Weights:

Centrifugal clutch weights can wear, affecting acceleration and engagement.

📚 Vehicle History

Yamaha Legacy:

Yamaha Motor Company, founded in 1955, has a long history in motorcycles, musical instruments, and other motorized products, known for innovation and quality.

Qt50 Lineage:

The QT50 was part of Yamaha's push into the growing moped and scooter market in the late 1970s and early 1980s, offering simple, reliable transportation.

Production Years:

The QT50 model line was produced for several years, with the 1979 model being an early iteration.

🏆 Awards & Recognition

Historical Acclaim:

While specific awards for the QT50 are unlikely to be found, it was a popular model in its segment for its reliability and affordability, contributing to Yamaha's strong market presence in the scooter category.