Tohatsu began producing a single-cylinder 50cc racing bike in 1962, called the Rumpet CR. See picture below, courtesy of Classic Racer (it's the one on the right) :
These were raced in the UK and in Switzerland. In the UK, the Simmonds brothers were the drivers. These machines were hopelessly uncompetitive and seized continuously. I remember seing one with its Swiss owner repairing the machine during a hillclimb at Freiburg. It was his third piston of the day.
Shortly after this, Tohatsu designed and built a 50cc twin-cylinder with a 5-speed gear change and dry clutch. Probably no more than 6 were ever built. The Simmonds got at least one, while another was in Switzerland. The others raced in Japan and Malaysia. Again they were slow and unreliable, but oh so pretty... a pair survives today and runs fine using modern alloys.
These were not fast enough to compete with the Suzuki, Honda or even the Derbi production racers of the time. Indeed they lacked the magic ingredient: a disc valve induction allowing much longer intake timing, as well as the magic "third" transfer port facing the exhaust. At the time, the Japanese were learning, fast. Tohatsu was not learning fast enough.
In 1964, Tohatsu also produced a very limited number of piston-port 125cc twins, the subject of the question above. These were beautiful machines with well designed chassis, large Honda-style brakes and 6-speed transmissions, but they could not really compete with even a good Bultaco TSS, let alone a Honda CR93. However Dave Simmonds was a heck of a good driver and won a few short-circuit races with his between it being broken. Eventually he ran out of spares and the Tohatsus were parked in favor of other Japanese machinery.
In France, Jacques Roca, the Derbi importer, got hold of one of those 125cc Tohatsus and replaced the seizing-prone cylinders by two from a Derbi 50c and a Derbi 75cc. The mix did not work too well either but was really fast while it lasted.
Tohatsu was at the time struggling for its existence and the racing programme had cost them dearly without the hoped for success. In 1965, Bridgestone absorbed Tohatsu and put its engineers to work on their own road and racing machines. The Bridgestone 175 and 350 roadsters were brilliant designs with disc valves, fast, reliable and handling well. But the other large Japanese motorcycle manufacturers did not see too well of their tire supplier competing with them, so in 1967 after Honda forced their hand, they closed their motorcycle production. A great loss in my opinion.
Regards,
T54