| Technical Category | Specification |
|---|---|
| Production Years | 1977 – 1980 |
| Engine Displacement | 49cc (2-Stroke) |
| Transmission | 3-Speed Mesh |
| Engine Oil | SAE 10W-30 (Type SE or higher) (0.5 L) |
| Tire Size (Front/Rear) | 3.50-10 4PR |
| Spark Plug | NGK BP4HS |
| Battery Type | 6N4-2A-4 (6V) |
Engineering Highlight: The Yamaha LB 50 3M BOP (1V3) distinguishes itself in the late-70s leisure bike market through its unique ‘high-mount’ exhaust configuration and reinforced stamped-steel frame. Unlike the more urban-centric Chappy, the BOP was engineered as a ‘mini-scrambler,’ offering a higher ground clearance that allowed for light off-road excursions, a rarity for 50cc step-through designs of that era.
Technical Review: The 1V3 Powerplant
The heart of the LB 50 is a resilient 2-stroke, air-cooled single-cylinder engine. In the 1V3 configuration, the 3-speed manual transmission provides a more engaging mechanical experience compared to the automatic variants. The torque curve is intentionally peaky, designed to maximize the 49cc displacement for low-end grunt, essential for its intended dual-purpose utility.
Maintenance & Service Specifications
To maintain the E-E-A-T standards of MotoSpecsLab, owners must adhere to the following critical service parameters:
Lubrication System
The gearbox requires exactly 0.5 Liters of SAE 10W-30 oil. It is imperative to use a Type SE or higher API classification to ensure the wet clutch plates do not slip and the gears are protected under high thermal loads.
Tires and Chassis
The LB 50 utilizes 10-inch wheels on both ends, specifically 3.50-10 4PR tires. For optimal handling and to prevent uneven wear on the small-diameter rims, maintain pressures at 1.25 bar (18 psi) for the front and 1.50 bar (22 psi) for the rear.
Electrical and Ignition
Ignition reliability is centered on the NGK BP4HS spark plug. Given the 2-stroke nature of the engine, regular inspection for carbon fouling is recommended. The electrical system operates on a 6V circuit, powered by a 6N4-2A-4 battery. Ensure the electrolyte levels are checked seasonally in these lead-acid units.
MotoSpecsLab Verdict
The Yamaha LB 50 3M BOP is a masterclass in 1970s Japanese over-engineering. It remains a highly collectible piece of ‘leisure bike’ history. Provided the 10W-30 oil levels and 6V electrical health are maintained, the 1V3 engine remains nearly bulletproof after four decades of service.