| Feature | Specification |
|---|---|
| Production Years | 1977 – 1980 |
| Engine Type | SOHC Parallel-Twin, 4-Stroke |
| Engine Oil | SAE 20W-40 (API SE) |
| Oil Capacity | 1.6 L (2.1 L dry) |
| Spark Plug | NGK BP7ES (Gap: 0.7mm – 0.8mm) |
| Battery | YB12A-A |
| Tire Pressure (F/R) | F: 1.8 bar / R: 2.0 – 2.3 bar |
Historical Engineering Highlight: The Yamaha XS 250 (1U5) holds a significant place in motorcycling history as Yamaha’s first major foray into the four-stroke 250cc market. While Yamaha was legendary for its two-stroke RD series, the XS 250 was engineered specifically to meet the growing demand for reliability and fuel efficiency in the late 1970s. It was one of the few 250cc machines of its era to utilize a 180-degree crankshaft design in a parallel-twin configuration, providing a unique exhaust note and distinct vibration characteristics that favored low-end torque over high-RPM screaming.
Technical Overview
The XS 250 (1U5) was built on a shared platform with its larger sibling, the XS 400. This over-engineering meant the frame and cycle parts were exceptionally robust for a 250cc machine. The SOHC engine featured two valves per cylinder and was fed by twin Mikuni carburetors, providing a smooth power delivery suited for urban commuting and light touring.
Maintenance Guide
1. Lubrication System
The XS 250 utilizes a wet-sump lubrication system. For optimal protection of the vintage internals, SAE 20W-40 oil meeting API SE standards is recommended. During a standard oil change, the engine requires 1.6 liters. If the engine has been completely disassembled (dry), the capacity increases to 2.1 liters.
2. Ignition & Electrical
Reliable ignition is critical for this twin. The factory specifies NGK BP7ES spark plugs. Ensure the electrode gap is precisely set between 0.7mm and 0.8mm. Electrical power is managed by a 12V system utilizing a YB12A-A battery, which provides sufficient cranking amps for the electric starter.
3. Chassis and Tires
The 1U5 model rides on 18-inch wheels front and rear.
- Front Tire: 3.00-18 4PR (Pressure: 1.8 bar / 26 psi)
- Rear Tire: 3.50-18 4PR (Pressure: 2.0 bar / 28 psi for solo; 2.3 bar / 33 psi for pillion/high speed)
Editorial Verdict
At MotoSpecsLab, we categorize the XS 250 – 1U5 as a ‘Bulletproof Classic.’ While it lacks the raw acceleration of the RD series, its mechanical simplicity and parts commonality with the XS 400 make it an ideal entry point for vintage motorcycle restoration. Proper attention to the cam chain tensioner and regular oil intervals will ensure this machine remains roadworthy for decades.