This document is a service manual for Yamaha motorcycles and motocyclettes, specifically covering models PW50L, PW50M, PW50N, PW50P, PW50R, PW50S, QT50F, QT50G, and QT50H, manufactured between 1979 and 2004. It provides comprehensive information for maintenance, inspection, and repair.
Function Description
The manual serves as a detailed guide for technicians and owners to perform various service operations on the specified Yamaha 50cc models. It covers general information, engine overhaul, carburetion, power train, chassis, and electrical systems, along with an appendix for specifications and wiring diagrams. The primary function is to ensure proper maintenance, reliable operation, and extended service life of the motorcycles.
Important Technical Specifications
The manual provides extensive technical specifications across various sections.
General Specifications:
- Model: 3L8
- Engine ID & Starting Number: 3L5-700101
- Dimensions:
- Overall Length: 1,550 mm (61.0 in)
- Overall Width (standard): 670 mm (26.4 in)
- Overall Height (standard): 965 mm (38.0 in)
- Seat Height: 705 mm (27.8 in)
- Wheelbase: 1,050 mm (41.3 in)
- Minimum Ground Clearance: 120 mm (4.7 in)
- Weight: Net Weight: 43 kg (95 lb)
- Performance: Minimum Turning Radius: 1,500 mm (59.1 in)
Engine Specifications:
- Engine Type: Air cooled 2-stroke, Gasoline, Reed valve
- Engine Model: 3L5
- Displacement: 49 cm³ (3.0 cu.in)
- Bore x Stroke: 40.0 mm x 39.2 mm (1.575 in x 1.543 in)
- Compression Ratio: 6.0 : 1
- Starting System: Kick
- Ignition System: C.D.I.
- Lubrication System: Separate lubrication (Yamaha Autolube)
- Cylinder Head Volume: 7.0 cm³ (0.43 cu.in)
- Cylinder Material: Special cast iron
- Bore Size: 40 mm (1.57 in)
- Taper Limit: 0.05 mm (0.002 in)
- Out of Round Limit: 0.01 mm (0.0004 in)
- Piston Clearance: 0.035 ~ 0.047 mm (0.0014 ~ 0.0019 in)
- Piston Over Size: 40.25 mm, 40.50 mm (1.585 in, 1.594 in)
- Piston Ring Design: Keystone ring (Top), Keystone ring (2nd)
- Piston Ring End Gap (Installed): 0.15 ~ 0.35 mm (0.006 ~ 0.014 in) (Top/Second)
- Piston Ring Groove Side Clearance: 0.03 ~ 0.05 mm (0.001 ~ 0.002 in) (Top/Second)
- Small End Bearing Type: Needle bearing
- Big End Bearing Type: Needle bearing
- Crankshaft Assembly Width (F): 38.00 mm (1.500 in)
- Crankshaft Deflection (A): 0.03 mm (0.0012 in)
- Connecting Rod Big End Side Clearance (C): 0.35 ~ 0.55 mm (0.014 ~ 0.021 in)
- Connecting Rod Small End Deflection (S): 0.4 ~ 0.8 mm (0.016 ~ 0.031 in)
- Crank Bearing Type: 6203-C3 (Left), 6202-C3 (Right)
- Crank Oil Seal Type: SD17-35-7 (Left), SD23-35-7 (Right)
- Clutch Type: Wet, Centrifugal automatic
- Primary Reduction Ratio & Method: 63/33 (1.909), gear
- Clutch Shoe Thickness: 1.0 mm (0.040 in)
- Clutch Shoe Spring Free Length: 34.5 mm (1.36 in)
- Clutch Shoe Spring Set Weight: 3.6 kg (7.9 lb)
- Clutch-in Revolution: 2,500 r/min
- Clutch-stall Revolution: 3,500 r/min
- Transmission Secondary Reduction Ratio & Method: 19/15 (1.266), bevel wheel gear
- Transmission Gear Oil Quantity & Type: Exchange: 300 cm³ (0.26 IMP.qt), Total: 350 cm³ (0.31 IMP.qt), Yamalube 4-cycle oil or SAE 10W/30 motor oil
- Reduction Ratio & Method: 57/10 (5.700), bevel wheel gear
- Kick Starter Type: Ratchet type
- Intake Air Cleaner Type: Oiled foam rubber
- Reed Valve Bending Limit: 0.8 mm (0.031 in)
- Valve Lift: 4.8 ± 0.2 mm (0.19 ± 0.008 in)
- Carburetor Type & Manufacturer: VM12SC, MIKUNI
- Carburetor ID Mark: 3L500 (3L501) (After engine serial No. 3L5-702401)
- Main Jet (M.J.): #75 (#70)
- Air Jet (A.J.): 2.5
- Jet Needle-clip Position (J.N.): 3D3-3 (3T3-2)
- Cutaway (C.A.): 1.0 (4.0)
- Pilot Jet (P.J.): #45 (#40)
- Air Screw (turns out): 1-3/4 (1-1/2)
- Starter Jet (G.S.): #35
- Fuel Level (F.L.): 22.0 mm ± 1.0 mm (0.87 ± 0.04 in)
- Engine Idling Speed: 1,700 r/min
- Autolube Pump Color Code: Yellow
- Autolube Pump-Minimum Stroke: 0.20 ~ 0.25 mm (0.008 ~ 0.010 in)
- Autolube Pump-Maximum Stroke: 0.95 ~ 1.10 mm (0.037 ~ 0.043 in)
- Oil Tank Capacity: 0.8 L (0.7 IMP.qt)
- Oil Grade: Yamalube 2-cycle oil or equivalent
Chassis Specifications:
- Frame Design: Steel tube underbone
- Steering System Caster: 25°
- Steering System Trail: 7.5 mm (2.95 in)
- Number & Size of Balls in Steering Head: 26 pcs 5/32 in (Upper/Lower Race)
- Lock to Lock Angle: 100°
- Front Suspension Type: Telescopic fork
- Front Suspension Damper Type: Coil spring
- Front Fork Cushion Travel: 45 mm (1.77 in)
- Front Fork Spring Free Length: 78.0 mm (3.86 in)
- Front Fork Spring Constant: k1 = 0.55 kg/mm
- Front Fork Wire Diameter x Winding Outside Diameter: φ3.2 mm x φ26.8 mm (1.06 in)
- Front Fork Inner Tube Outside Diameter: φ22.2 mm (0.87 in)
- Rear Suspension Type: Unit swing
- Rear Suspension Damper Type: Coil spring, Oil damper
- Rear Shock Absorber Travel: 30 mm (1.18 in)
- Rear Wheel Travel: 50 mm (1.97 in)
- Rear Shock Absorber Spring Free Length: 150.5 mm (5.93 in)
- Rear Shock Absorber Spring Set Length: 145.5 mm (5.73 in)
- Rear Shock Absorber Spring Constant: k1 = 6.32 kg/mm
- Rear Shock Absorber Spring Wire Diameter x Winding Outside Diameter: φ6.4 mm x φ39.0 mm (1.54 in)
- Fuel Tank Capacity: 2.3 L (0.5 IMP.gal)
- Fuel Grade: Regular leaded gasoline
- Wheel Tire Size (Front/Rear): 2.00-14-4PR, 2.25-14-4PR
- Wheel Tire Pressure (Front/Rear): 1.25 bar (1.25 kg/cm², 18 psi), 2.0 bar (2.0 kg/cm², 28 psi)
- Wheel Rim Size (Front/Rear): 1.20 x 14, 1.20 x 14
- Wheel Rim Run Out Limit (Front/Rear Vertical/Lateral): 0.7 mm (0.028 in), 1.3 mm (0.051 in)
- Drive Shaft Lubricating Grease & Quantity: Lithium base wheel bearing grease (Ex. SHELL LETHINAX A), 10 g (0.4 oz)
- Brake Front/Rear Type: Drum brake
- Brake Drum Diameter: φ80 mm (3.15 in)
- Brake Shoe Diameter x Width: φ80 x 17 mm (3.15 x 0.67 in)
- Brake Lining Thickness/Wear Limit: 3.5 mm/2 mm (0.138 in/0.079 in)
- Brake Shoe Spring Free Length: 44.5 mm (1.75 in)
Electrical Specifications:
- Ignition System Model/Manufacturer: F3L6/Yamaha
- Ignition System Voltage: 6V
- Ignition System Pulser Coil Resistance (White/Red-Black): 20Ω ± 10% at 20°C (68°F)
- Ignition System Charge Coil Resistance (Black/Red-Black): 295Ω ± 10% at 20°C (68°F)
- Ignition Timing: 0.94 mm (0.037 in) (Not adjustable)
- Ignition Coil Model/Manufacturer: C2T4/Yamaha
- Ignition Coil Spark Gap: 7 mm (0.28 in)
- Ignition Coil Primary Winding Resistance: 1.6Ω ± 10% at 20°C (68°F)
- Ignition Coil Secondary Winding Resistance: 6.6kΩ ± 20% at 20°C (68°F)
- Ignition Coil Diode: No
- Spark Plug Type/Manufacture: BP4HS (N.G.K.)
- Spark Plug Gap: 0.6 ~ 0.7 mm (0.024 ~ 0.028 in)
- C.D.I. Unit Model/Manufacturer: 2E9-Mo/Yamaha
- C.D.I. Magneto Model/Manufacturer: F3L6/Yamaha
- Charging System Type: Flywheel Magneto
- Charging System Charging Output: 1.0 ± 0.5A/5,000 r/min, 1.7 ± 0.5A/8,000 r/min
- Charging System Charge Coil Resistance (Black-White): 0.38Ω ± 10% at 20°C (68°F)
- Charging System Lighting Output: 6.5V or more/4,000 r/min, 7.7V or less/8,000 r/min
- Charging System Lighting Coil Resistance (Black-Blue): 0.28Ω ± 10% at 20°C (68°F)
- Rectifier Type: DE4504, S5108
- Rectifier Capacity: 4A
- Rectifier Withstand Voltage: 200V
- Rectifier Rating: Silicon
- Battery Model/Manufacture: 6N4-2A-2/GS, FURUKAWA, YUASA
- Battery Capacity: 6V-4AH
- Battery Charging Rate: 0.4A x 10 hours
- Battery Specific Gravity: 1.26 at 20°C (68°F)
- Lighting System Headlight Type: Semi-Sealed beam
- Lighting System Headlight Wattage: 6V, 20W/20W
- Lighting System Tail/Stop Light Wattage: 6V, 5.3W/25W
- Lighting System Flasher Light Wattage: 6V, 17W
- Lighting System Flasher Pilot Light Wattage: 6V, 3W
- Lighting System Meter Light Wattage: 6V, 3W
- Lighting System High Beam Indicator Light Wattage: 6V, 3W
- Lighting System Oil Warning Light Wattage: 3V, 3W
- Horn Model: GF-6
- Horn Maximum Amperage: 1.5A
- Flasher Relay Model: FR6T11
- Flasher Relay Type: Heat-Ribbon type
- Flasher Relay Flasher Frequency: 90 cycles/min
- Fuse Rating/Quantity: 10A/1 pc
Usage Features
The manual is structured to facilitate ease of use for various service tasks. Each major system (Engine, Carburetion, Power Train, Chassis, Electrical) is broken down into chapters, with detailed sub-sections for specific components and procedures.
- Clear Identification: The manual begins with machine identification, showing the location of the frame and engine serial numbers, which is crucial for parts ordering and service history.
- Special Tools: A dedicated section lists and illustrates specialized tools required for specific maintenance and repair tasks, complete with their Yamaha tool numbers. This ensures that technicians use the correct equipment, preventing damage and ensuring accurate work.
- Step-by-Step Procedures: Most procedures are described in a step-by-step format, often accompanied by diagrams and photographs to guide the user. This includes removal, disassembly, inspection, repair, assembling, and installation processes.
- Dual Language: The manual is presented in both English and French, making it accessible to a wider range of users.
- Detailed Illustrations: Numerous exploded views, diagrams, and photographs are integrated throughout the manual to visually clarify component locations, assembly sequences, and inspection points.
- Torque Specifications: Critical fasteners have specified tightening torque values, ensuring components are secured correctly to prevent loosening or damage. These are listed in a dedicated section in the appendix and also within relevant repair sections.
- Troubleshooting: While not explicitly detailed in the provided table of contents, service manuals typically include troubleshooting guides to help diagnose common problems.
Maintenance Features
The manual emphasizes periodic inspection and adjustments to ensure the motorcycle's longevity and performance.
- Maintenance Intervals: Detailed charts outline the recommended maintenance intervals for various components, categorized by initial service (1, 3, 6 months) and thereafter (every 6 months or annually). These intervals cover:
- Cylinder head/Exhaust system: Decarbonize
- Spark plug: Inspect/Clean/Replace
- Air filter: Clean/Replace
- Carburetor: Check/Adjust/Clean
- Autolube pump: Check/Adjust/Air bleeding
- Brake system (complete): Check/Adjust/Repair
- Wheels and tires: Check pressure/Wear/Balance/Run out
- Suspension system: Check/Repair
- Steering lock: Check
- Battery: Top-up/Check specific gravity and breather pipe
- Lights/Signals: Check operation/Replace
- Fittings/Fasteners: Tighten
- Lubrication Intervals: A separate chart specifies lubrication intervals for components like:
- Transmission oil: Replace/Warm engine before draining
- Control and meter cables: Apply thoroughly
- Throttle grip and housing: Apply lightly
- Brake lever: Apply lightly
- Brake cam shaft: Apply lightly
- Steering bearings: Inspect/thoroughly/Pack moderately
- Speedometer gear housing: Inspect/thoroughly/Pack moderately
- Wheel bearings: Do not over-pack/Apply
- Middle and final gear: See page 5-9 to repack grease
- Fluid Specifications: The manual specifies the types and quantities of fluids required, such as Yamalube 4-cycle oil, SAE 10W/30 motor oil, Yamalube 2-cycle oil, and Lithium base wheel bearing grease.
- Component-Specific Maintenance: Each chapter provides detailed instructions for inspecting, cleaning, adjusting, and replacing parts within that system. For example:
- Carburetor: Instructions for pilot air screw adjustment, throttle stop screw adjustment, air cleaner cleaning, autolube pump bleeding, and minimum pump stroke adjustment.
- Engine: Procedures for engine oil (Autolube oil and Transmission oil) checks and changes, cylinder head and nut torque specifications.
- Chassis: Adjustments for front and rear brakes, inspection of brake shoe wear, drum inspection, brake shoe plate inspection, wheel bearing replacement, front wheel installation, rear wheel inspection, and steering head adjustments.
- Electrical: Ignition timing checks, spark plug inspection and gap adjustment, battery maintenance (level, specific gravity, charging), and headlight beam adjustment.
- Safety Warnings: Important safety warnings and cautions are highlighted throughout the manual to prevent injury to the technician and damage to the motorcycle. For instance, warnings about handling battery electrolyte and the importance of proper ventilation.
- Wear Limits: Critical components have specified wear limits, allowing technicians to determine if a part needs replacement rather than just adjustment or cleaning. Examples include piston ring end gap, crankshaft deflection, clutch shoe thickness, and brake shoe wear limit.
Overall, this service manual is an indispensable resource for anyone involved in the maintenance and repair of the listed Yamaha 50cc motorcycles, providing all the necessary information to keep them in optimal condition.
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