Royal Refinement
With exhaust systems still causing issues, an unorthodox solution from Kel Carruthers helped to cement Yamaha’s iconic TZ750 in the racing history books
Despite the outstanding successes of both Giacomo Agostini and Kenny Roberts at Imola, Yamaha’s TZ750 exhaust systems were still giving issues. Revised systems sent from Yamaha’s race shop back in Japan to Italy had failed to address the consistent fracturing of pipes and cones. There was also the ongoing concern with the compromised geometry of the exhaust under the engine. To get the four individual chambers to fit and allow decent angles of lean the outer faces had had to be flattened; this seriously affected power output. Team manager, former world champion and motorcycle guru Kel Carruthers, steered what was a pragmatic solution through development and prototyping. The left exhaust system was reconfigured to run upwards and across the gearbox of the engine and below the bank of four carburettors. From here it then exited the chassis on the righthand side, giving an asymmetric tail end. If, in theory, running an exhaust perilously close to carburettors should have compromised their action and breathing, little actually came of this unorthodox approach and remained the chosen layout until the mighty TZ was finally pensioned off.
Henceforth the TZ750 began to rule the race tracks with only occasional upsets from Suzuki’s TR750 and Kawasaki’s H2R cum KR750. Despite being well researched, the early 750s still experienced some material failures. With the bike being literally at the forefront of race bike design at the time, some of problems were obscure yet effectively show stoppers. The teeth on both oil and water pumps could strip; overheating issues were tracked down to then thermostats not functioning correctly; main bearings were being pushed beyond their capabilities; and cylinder head nuts sometimes broke in use. Yamaha were still on a learning curve but, predictably, they also had an ace up their corporate sleeves.
Halfway through the 1974 TZ750B model run the bike increased in capacity from its old, TZ350 origins, to a full 750 instead of 700ccs. Lessons learnt had been applied and the water pump teeth problem was resolved, and minor revisions to the cogs in the gearbox were carried out. On paper those upgrades didn’t seem like much, yet the final TZ750Cs of 1975 were now offering 130bhp – some 15 horses up on the ‘old’ 700. In reality the later B and all C models were an interim development before the factory team rolled out their 1975 Daytona fleet. This trio showcased the firm’s moto-cross derived monoshock rear end, which substantially reduced the old tail end weave at speed associated with the twin shock models. Giacomo Agostini, Kenny Roberts and Steve Baker were the lucky recipients of the new model, but things didn’t go to plan. Roberts’ bike went out with clutch issues, allowing Geno Romero to take first on a twin shock 750. Steve Baker came home a creditable second with Agostini hampered with carburation issues in fourth. It was still, however, another Yamaha fest when Johnny Cecotto miraculously rode one of the early, two pipes per side, 700s to third place.
Within America the TZ750 was now the dominant race bike, regularly and consistently mopping up at almost every race and generally belittling the factory efforts of both Kawasaki and Suzuki. Over in Europe it was a similar, but not quite so definitive, situation with occasional upsets for the now virtually predominant TZ750. Barry Sheene still scored a trio of F750 victories and factory Kawasaki riders Mick Grant and Barry Ditchburn on their water-cooled triples were still mixing it amongst the big Yamahas.
The only circuit yet to fall to the big TZ was the Isle of Man TT where the 750’s excessive power, bulk and weight simply made it too unwieldy… not that this worried Yamaha much. Against all expectations a Yamaha 350 twin ridden by John Williams beat the 750s. The tuning fork brand was most emphatically on a roll.
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