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The Yamaha TX750 was produced only for 2 years in 1973 and 1974. It was loosely based on the XS650 but had what Yamaha called an "Omni-Phase balancer" to counter vibrations which are inherent in a parallel twin with the crankshaft set at 360 degrees (both pistons rise at the same time). Using a pair of balancers (one clocked to counter the primary imbalances of the cylinders, the other to counter the rocking coupling created by the first balancer), Yamaha’s Omni-Phase balancer system all but eliminated vibration in the TX750, giving the new engine the kind of smoothness previously thought possible only in a triple or a four cylinder. This new system was a first for a Motorcycle but resulted in massive failures for the first model year. Although, these problems were fixed in 1974 sales never picked up and the machine was shelved.
Cycle World magazine, in their October 1972 issue positively reviewed the concept when they wrote: “The result is smoothness beyond belief,” . “Shut your eyes and you are on a four. It couldn’t be a twin.” In addition, the bike was set up with a single front disk brake with provision to install a second one on the other side. European machines were delivered with twin disk brakes from the factory. The bike also had an interesting warning light system with a brake pad wear indicator, a first for a motorcycle.
The bike was popular at first but soon reliability problems began to emerge and the problems lay with the Omni-Phase balancer: At high rpm the balance weights would whip oil in the sump into a froth, aerating the oil and starving the crank for lubrication which resulted in bearing failure.
In addition, the balance chain would stretch, resulting with the counterweights being out of phase and making the engine run rough. Although Yamaha quickly repaired the problems, including a deeper sump and an adjustable balance chain, sales fell and the TX750 became synonymous with poor design and reliability. The 1974 Model was extensively modified with a revised sump and does not suffer from reliability issues.
The TX750 is not a popular classic motorcycle at present and it can be acquired at quite low value. Like with most vintage Yamaha motorcycles parts can be an issue compounded by the fact that the bike was produced for only two years.