Yamaha's New Four... Tokyo
Yamaha's New Four... TOKYO
11 to HE favor TOKYO a different MOTOR motorcycle show seems manufacturer each year. It was Yamaha's turn this time and they filled the limelight with a new 750 two-stroke fourcylinder roadster.
The rakish machine is jammed with just about every possible gimmick for performance and sex appeal. It is watercooled for even cylinder temperatures and quiet running. It is reed-valved for flexibility and low-speed pulling power. And it has the first dual-disc front brake ever fitted as standard for a mass production motorcycle.
The Yamaha GL750, as it is called, also has a form of fuel injection operated by a diaphragm pump, which makes use of negative pressure pulses in the crankcase.
Actual displacement of the GL750 is 743cc, with bore/stroke measurements of 65 by 56mm. Rated at 70 bhp at 7000 rpm, with a dry weight of 451 lb., it should prove quite fast.
Along with the other three Kawasaki three-cylinder two-strokes was introduced a 250 Three, which has the distinction of being the first production Three ever made in that size.
The bonus for that extra bit of complexity is a high power rating, a claimed 32 bhp at 8000 rpm.
The 250 Three is air-cooled, following the same basic design specifications as its bigger relatives. In fact, it appears to be little more than a sleeved-down version of the 350 S2, for both 250 and 350 have the same 52.3-mm stroke. The 250's bore is only 45mm, making it somewhat "undersquare."
Making bore smaller than stroke may seem a curious way to go in the horsepower race. But two models which share a common bottom end save tooling costs for Kawasaki and, perhaps, the consumer. And with a single piston displacement of only 82cc, you can hardly complain about the design on the basis of either piston speed or reciprocating inertia. Kawasaki's 250 and 350 enduro Singles have a similar arrangement, and the 250 seems to suffer not at all.
Both the Yamaha 750 and the Kawasaki 250 Three should provide great interest for the road rider, as well as for spectators when the racing versions of these bikes come along.
Yamaha will undoubtedly get around to racing the 750 Four in the AMA big bore class, but not this year, as the necessary 200 machines were not in the U.S. in time for AMA approval.
...And A Kawasaki 250 Three P1`I•~_n 4 ;
