Suzuki GS4OO four-stroke an impressive performer

Press, 9 December 1976, Page 22

Suzuki GS4OO four-stroke an impressive performer

By

ROD DEW

The entry of the Suzuki factory into the valve motor field after more than 15 years of two-stroke specialisation was awaited in certain quarters with some trepidation. But the ability to do the job right at the first attempt has not deserted the Japanese Suzuki designers. The new GS7SO four and smaller GS4OO twin four-strokes, which are now on New Zealand showroom floors, are at least as good as anything produced by other manufacturers in their class. The GS4OO, w'bich is virtually a GS7SO without the two end cylinders, is at $1999 exactly $1199 cheaper than its big brother and if for no other reason than this must be expected to command the largest share of Suzuki’s potential four-stroke market. Because of this, the 398 cu. cm twin was chosen for the subject of this test. A considerable amount of publicity material preceded the twin to New Zealand. Some of it was exaggerated, but no more than a few kilometres on the GS4OO provided by Velvin and Cressweil, Limited, was needed to appreciate that there was also plenty of substance behind the majority of the factory’s claims. It has more power and performance than other

twin-cylinder machines in the same capacity range and compares very' favourably with the Honda 400 four—regarded by many as the ultimate in mid-range roadster design. The power characteristics of the double overhead camshaft motor are impressive, to say the least.

The engine will pull away in top gear from 1800 r.p.m. without snatch. Acceleration is brisk at low engine speeds. The charactistics of the motor could fairly be compared with that of a big single. But when the engine speed passes 5000 r.p.m. these

characteristics undergo a remarkable transformation. DUAL CHARACTER The bike suddenly adopts the identity of a spirited two-stroke or highly- tuned four-stroke four. Even the exhaust note changes from a solid burble to a low-pitched howl. It is not exactly the same as having the best of two worlds. But it comes as close to providing this as any other machine 1 have ridden in a decade of road testing motor-cycles. The motor will rev quite freely up to the red danger area on the tachometer of 9000 r.p.m. And there is hardly a hint of vibration at any speed. It is as smooth as one could hope for any in-

temal combustion engine to be. This is the result of a number of contributing factors. The two crankpins have been arranged 180 deg. apart, a crankshaft counterbalancer is incorporated and a variable-venturi twin carburettor is Used. The counter - balancer operates on principles quite different from those of conventional counterbalancing units. The centriflcal forces are cancelled indirectly by providing a separate unbalanced shaft. And there can be no doubt that it works magnificently. HIGH PERFORMANCE There is no doubt, either, that the double overhead camshaft engine is of the high performance variety.

It has a top speed in excess of 165 km/h (103 m.p.h.) and in all performance figures compares very- favourably with the Suzuki factory's mid range “rocket”, the GT3BO threecylinder two-stroke. The GS4OO produces 36 brake horsepower at 8500 r.p.m. (just one less than the GT 380, which achieves its peak at 7500 r.p.m.). Maximum torque for the GS4OO is 3.20kg/m (23.2ft--1b) at 7500 r.p.m. compared to 3.81kg/m (26.7 ft-lb for the GT3BO. Another merit point in favour of the GS4OO is that its external engine surfaces are of polished alloy — not paint. The recent trend towards painted surfaces on engines is not to be encouraged. It marks easily and engines rapidly take on a very shabby appearance. Polished surfaces are also much easier to clean. The transmission is sixspeed (one more ratio than on the GS7SO) and this is ideally suited to the characteristics of the motor. The box is smooth and clutchless racing changes are simple. There w’ere three minor points about the GS4OO which I did not particularly like. Th,e fast back style of seat, a concession to current fashions, would make it very difficult to fit a substantial carrier, the seat is a little too hard for long distance touring and the front telescopic forks "clonk” as they hit the stopper when fully extended. GOOD HANDLING This latter fault can be irritating, although it in no way affects the handling, which is excellent. On rough or smooth, straight or winding, the Suzuki is a joy to ride. The cradle frame with its twin down tubes holds the bike firmly together. Unlike the GS7SO, the GS4OO has retained the drum brake at the rear. The braking on the front wheel is by a single hydraulic disc. The combination is well matched and could not be faulted under test conditions. Unlike its rivals, Suzuki has preferred the twin exhaust system to the single and this certainly gives the bike a balanced look. The locking cover over the petrol filler cap has, however, been copied from i others. This is another conces- I sion to fashion. It is a lot I harder to put fuel into the I tank now than it is to get I it out. Any enterprising I thief merely'needs to yank a fuel lead off and run the fuel into a tin. This is, nevertheless, an indication of the pains Suzuki has taken to produce a first-class motorcycle. in this aim it has undoubtedly succeeded. Starting is electric or kick and there is now the familiar Suzuki gear position indicator nestling among the instruments on the handlebars. Generally, the new Suzuki four-stroke is an excellent roadster with a i high standard of engineer- ' ing. If it is an indication of the standards Suzuki in- i tends to set with its new four-stroke range then it deserves a considerable measure of success.