| Parameter | Specification |
|---|---|
| Model Code | 1T5 |
| Production Years | 1977-1978 |
| Engine Type | 826cc / 747cc Inline-3, 4-stroke |
| Engine Oil | SAE 20W-40 (API SE+) / 3.5 L |
| Front Tire | 3.25 H 19 (1.8 bar / 26 psi) |
| Rear Tire | 4.00 H 18 (2.0 bar / 28 psi) |
| Spark Plug | NGK BP7ES (Gap: 0.7–0.8 mm) |
| Battery | 12N14-3A |
The Yamaha XS 750/E (1T5) represents a pivotal moment in Japanese motorcycle history. While the industry was obsessed with four-cylinder configurations, Yamaha engineered a sophisticated 120-degree crankshaft triple that offered the narrow profile of a twin with the smoothness of a four. A unique engineering highlight of the 1T5 series was its integration of a constant-velocity (CV) carburetor setup and a maintenance-free shaft drive, earning it the nickname ‘The Bargain BMW’ among contemporary journalists.
Technical Engineering Overview
The 1T5 variant, specifically the ‘E’ model, addressed several early teething issues found in the 1976 ‘C’ models. The engine utilizes a Double Overhead Cam (DOHC) design, which was advanced for its time. The 120-degree crank spacing provides inherent primary balance, resulting in a distinctive exhaust note that remains one of the most celebrated sounds in motorcycling. The shaft drive system was engineered for longevity, utilizing a secondary gear case that requires periodic inspection but offers significantly lower maintenance than chain-driven rivals.
Maintenance & Service Guide
Lubrication System
To maintain the thermal stability of the center cylinder—which typically runs hotter on air-cooled triples—high-quality oil is non-negotiable. The XS 750/E requires 3.5 Liters of SAE 20W-40. Ensure the oil meets or exceeds API Service SE standards. Given the age of these machines, modern synthetic blends with high ZDDP content are often preferred to protect the flat-tappet cam followers.
Ignition and Electrical
The 1T5 utilizes NGK BP7ES spark plugs. For optimal combustion and throttle response, the electrode gap must be precisely set between 0.7 and 0.8 mm. The electrical system is supported by a 12N14-3A battery; owners should regularly check the electrolyte levels and terminal tension, as the early Yamaha charging systems are sensitive to voltage drops.
Tires and Handling
The handling characteristics of the XS 750 are defined by its 19-inch front and 18-inch rear wheel combination. For the standard 3.25 H 19 front and 4.00 H 18 rear tires, MotoSpecsLab recommends pressures of 1.8 bar (26 psi) and 2.0 bar (28 psi) respectively for solo riding. Correct pressure is critical to mitigate the ‘shaft-effect’ (chassis rising under acceleration) inherent in early shaft-drive designs.
Editorial Verdict
The Yamaha XS 750/E – 1T5 is a connoisseur’s vintage motorcycle. It lacks the raw aggression of the Kawasaki triples but offers a level of mechanical refinement and ‘long-legged’ touring capability that was decades ahead of its time. For the modern collector, the 1T5 is the ‘sweet spot’ in the XS750 production run, offering the best balance of the original styling with improved mechanical reliability.