Yamaha introduced the water-cooled TZ series in June 1973, replacing the earlier air-cooled TD1 and TD2 series. The production-volume racer was based directly on the OW17 factory machine used in Grand Prix competition, from which Dieter Braun won the 250 cc world championship in 1973. A near-identical variant, the Yamaha TZ350, was produced simultaneously with a larger bore of 64 mm compared to the TZ250's 54 mm, for use in the 350 cc class.
The original water-cooled TZ250A used a bore-stroke ratio of 54 × 54 mm, carried over from the 1972 air-cooled TD3. Its parallel twin-cylinder layout, thyristor magneto ignition, and two-stroke architecture delivered 51 hp at launch. The engine drove a six-speed gearbox via chain to the rear wheel.
Early chassis used a double-loop tubular frame with conventional telescopic forks. The original braking system used a Duo-duplex drum at the front and a duplex drum at the rear. With the 1975 TZ250C model, the chassis was substantially revised: a cantilever swingarm with central spring strut replaced the earlier twin-shock arrangement, and disc brakes were introduced front and rear. The fuel tank held 23 litres with an oil supply of 1.5 litres.
In 1981 the TZ250H introduced a completely new design. Yamaha replaced the modified standard engine housing with a sand-cast housing developed specifically for racing. The two cylinders, previously cast as a single block, were redesigned to stand individually. Bore and stroke changed to 56 × 50.7 mm. Critically, the new engine incorporated the Yamaha Power Valve System, a variable exhaust valve mechanism that optimised power delivery across a wider rev range. Inlet diaphragm control, already used in Yamaha's road models, was adopted in the TZ engine from the TZ250N model onward.
By the final expansion of the original series — the TZ250A (3TC) introduced in 1990 — power output had reached 76 hp, representing a 49 percent increase over the original 1973 model through two decades of continuous development.
In 1991, Yamaha thoroughly revised the TZ250 engine to align it more closely with the contemporary factory YZR250 GP machine. The most significant change was the adoption of a V-engine configuration, departing from the parallel-twin layout that had defined the TZ series since 1973. This revised generation was produced and delivered to selected riders until 2004, when the 250 cc two-stroke class began its long wind-down as the FIM progressively shifted focus toward four-stroke machinery.
The TZ250 represents one of the longest continuous lineages in customer racing motorcycle production, spanning more than three decades from its 1973 introduction to final deliveries in 2004. Its availability to private teams and independent riders made it the backbone of 250 cc class grids throughout the 1970s, 1980s, and 1990s, and it produced multiple world champions during the era when the TZ platform underpinned much of the class. The model's close connection to Yamaha's factory efforts — in engine architecture, power valve technology, and chassis philosophy — meant that competitive privateers could access machinery that was genuinely close in specification to works-supported entries, a distinguishing quality that cemented the TZ250's reputation in road racing history.