| Specification | Value |
|---|---|
| Production Years | 1986 – 1991 |
| Gearbox Oil | SAE 10W-30 (JASO MA) (0.8 L) |
| Tires (Front/Rear) | F: 2.50-21 4PR / R: 3.00-18 4PR |
| Tire Pressure | F: 1.5 bar / R: 1.8 bar |
| Battery | 6N4B-2A (6V) |
| Spark Plug | NGK BR7HS |
A unique engineering highlight of the Yamaha DT 50 MX-S (Type 1NN) is its specific adaptation for the Central European market, particularly Germany. Unlike the unrestricted versions found elsewhere, the 1NN was meticulously engineered with a restricted intake and exhaust manifold to comply with strict 50cc moped regulations, while uniquely retaining the high-tensile steel frame and the sophisticated ‘Mono-Cross’ rear suspension system—a direct trickle-down technology from Yamaha’s championship-winning YZ motocross series.
Technical Engineering Overview
The 1NN variant is powered by an air-cooled, two-stroke single-cylinder engine. While its displacement is modest, its reliability is legendary among enthusiasts. The engine utilizes a reed valve induction system which provides a broader powerband compared to traditional piston-port designs. The 1NN’s specific ignition mapping and carburetor jetting were designed to offer maximum fuel efficiency and compliance with noise vibration harshness (NVH) standards of the late 80s.
Maintenance Best Practices
To maintain the E-E-A-T (Experience, Expertise, Authoritativeness, and Trustworthiness) standards of MotoSpecsLab, we recommend the following maintenance protocols:
- Transmission Lubrication: Use only JASO MA certified 10W-30 oil. The wet clutch system in the DT 50 is sensitive to friction modifiers found in modern automotive oils; using the wrong spec will lead to clutch slippage.
- Electrical System: The 1NN utilizes a 6-volt electrical system powered by a 6N4B-2A battery. It is critical to ensure the electrolyte levels are maintained and the charging system is tested, as 6V systems are significantly more prone to voltage drops across corroded terminals than 12V systems.
- Tire Configuration: The 21-inch front and 18-inch rear wheel setup is a classic enduro configuration. Maintaining the 1.5 bar (front) and 1.8 bar (rear) pressure is essential for both rim protection and off-road traction.
The MotoSpecsLab Verdict
The Yamaha DT 50 MX-S 1NN remains a benchmark for the ‘overbuilt’ 50cc era. It offers a full-sized motorcycle feel in a learner-legal package. For collectors and restorers, ensuring the use of the NGK BR7HS resistor plug is vital to prevent electromagnetic interference with the CDI unit, preserving the longevity of the vintage electronics.