The TZ750 story begins during the latter part of 1970 when Yamaha felt upstaged by the other Japanese manufacturers progress with large capacity Superbikes. Honda had the CB750, Suzuki the GT750 and Kawasaki the H2, while the nearest that Yamaha had to a big bike was the hopelessly outclassed XS twin and they vowed to do something about the situation. Of course all three of the former machines were produced in race form too spotlighting each factories efforts to the full.
What Yamaha came up with for the following year was a mock up of a four-cylinder two-stroke roadster, the GL750, this was displayed at the Tokyo show and also made its way to Europe for an airing at the Paris show. The GL was basically a fuel-injected stroker, forced into an XS650 rolling chassis, it is not known if this futuristic machine ever ran as a working mode,l but one thing is for sure it laid the foundations for what came next.
Its hard to imagine how much under pressure the development team at Yamaha were under, they had the GP 500s to develop along, with the two types of racing twins, the TZ and OW series, so to come up with an all new machine would have been hard to say the least but strive they did. By the end of 1973 the new 750 racer was ready to be viewed in public and took its place on the Yamaha stand at the Tokyo show of that year. F750 racing was meant to be for converted road machines, most likely to help the Harley Davidson racers in the US, and to that end at least 200 had to have been manufactured and sold to the public to be eligible. This is where Yamahas thinking gets radical as, unlike the opposition who simply produced hotted-up Factory run versions of their roadsters, Yamaha chose to create something that indeed was available to all, and yet completely unique and ultra competitive.
This effectively made the staggering TZ750 a production model and with it eligible for F750 competition. The first TZ four, actually just 698cc, made its mark at Daytona in 1974, piloted by the Yamaha new boy Giacomo Agostini, he rode from pole position to a stunning win, before embarking upon his first season as a two stroke GP rider. Before long the grids were awash with big Yams, 260 left the production line during that first year, and the type enjoyed an unprecedented run of success over the next decade.
Thought by many to be two TZ350 twins mated in the middle, in actual fact the 750 remains a scaled up version of the OW19 and 20 500cc GP racers, with no common parts shred with its smaller capacity siblings.
The type wasn’t without its problems however, the TZ was labelled a production machine but it used components completely unique to itself, the gearbox was notoriously difficult to get right without compromising one gear or another, while the twin shock chassis lacked high-speed stability prompting many to use after marker frames and parts. Even simple tasks like setting the ignition timing becomes a compromise with the 750, the CDI ignition is driven from the opposite end of the clutch jack shaft, meaning allowances have to be made with the gear lash within the system. Once sorted, the engine is pretty bullet-proof, rings can last many miles and piston wear is negligible too, the power plant runs backwards so the pistons drive nicely into the exhaust part of the cylinder and not the unsupported inlet.
For the mid point of 1975, half way through the B’s production run, the engine grew into the full 747cc, larger diameter pistons providing the extra CC’s and with it a healthy increase in power too. The first TZ was an under stressed and relatively tame beast to ride however with the oppositions response, and huge hikes in horsepower, the Yam four easily handled the later mods and tuning efforts. Although most TZ750s were simply over the counter models there was always the factory produced OW versions, to the untrained eye just better prepared racers but to those in the know these were exotic machines that the privateer could never afford to buy or run.
The OW series turned a significant corner in 1976 with the now legendary OW31, just five of these machines were produced and only the chosen few received them. Johnny Cecotto, Kenny Roberts, Agostini, Hideo Kanaya and Steve Baker being the lucky guys and what a package they got, bristling in exotic metals making it 18kgs lighter than a standard TZ and with around 20bhp more on tap the combination was hard to beat. The factory chassis departed from the twin shock design in 1975 but for the OW31 it got lower, more compact and a lot stiffer enabling the factory riders to dominate where ever they rode providing the tyres held up. Daytona 1976 and on the OW31s first outing Kenny Roberts was timed at 182mph, although he had to pit late in the race to change rapidly wearing rubber, Cecotto’s OW did take the win however although it too was in a bad way mechanically by the end of the race.
For the 77 season Yamaha produced thirty of what most thought would be a replica of the OW31, it looked spot on but close inspection revealed the TZ750D to be little different engine wise to the B and C models, the chassis was a vast improvement however although the over the counter model did lack the titanium, magnesium and other such exotic metals used in the factory version. In the UK the D model sold for £6500 and only five were sold officially in 77, many more did arrive in the country courtesy of private importing, and the machines that got left behind by the Yanks after the Easter match races. There was also the option to purchase just the engine from Yamaha and create your own racer, which many did especially for sidecar racing, £3500 being the asking price for the power plant complete with ignition.
The type did see two more years of production although no one realised at the time that the D was actually the end of the line as far as development went. 162 E models followed, technically unchanged for 1978, while a few F’s did appear for the following season, these being little more than D and E models assembled out of the remaining parts. For 1980 the F750 class changed the rules no longer requiring 200 models to be produced to be eligible and this opened the floodgates for all manner of over bored GP racers and trick specials, the newer machines up to date development and massive investment easily outstripping the dated technology of the TZ750, the big yam hung around for a few more seasons proving still reliable and competitive in the right hands but the writing was on the wall. Just around the corner was the newly emerging four-stroke Superbike racing, which in turn would become WSB, there was simply no need for the big stroker, although it had enjoyed a stunning run of success.
Those that have ridden her love the sweet engine, almost endless power and ease of use. Christened “The Beast” by those who hadn’t live with the type, in actual fact the big Yam is a delight to be on track with, surprisingly tractable and, while not a tool for the faint hearted, quite easy to live with and ride very fast.
Yamaha TZ750D Specifications
- Engine Liquid cooled two-stroke inline-four reed-valve induction
- Capacity 747cc cc
- Bore/stroke 66.4 x 54mm
- Power 110bhp @ 10500rpm
- Torque 55ft-lb @ 7500rpm
- Carburation 4 x Mikuni VM34
- Ignition Hitachi CDI
- Transmission 6-Speed dry clutch chain final drive
- Frame steel tube twin loop
- Suspension 36mm telescopic forks, Yamaha Monoshock
- Brakes 300mm discs two-piston calipers, 300mm disc two-piston caliper
- Wheels 3.25 x 18 3.50 x 18
- Weight 157kgs
- Top speed 175mph + (depending on gearing)
- Wheelbase 1407mm
- Fuel capacity 29lts