Suzuki GS 650GT

1981 Review

At first glance, you'd think there's nothing much new about Suzuki's new shaft-drive 650 fours. Certainly the Katana styling of the GS650G sticks out a mile, but underneath the novel bodywork there's still that same classic Suzuki accent on the engine that allows the more conventionally-styled GS650GT to blend inconspicuously into any line of Suzukis. That's no surprise. The factory has developed an understandably cautious approach to motorcycle development, one that places each new model just one step beyond the last. But there's enough in the new bikes to suggest both a fresh line of thought at Hamamatsu, as well as links with the past.

For a start, the 650s share a similar appearance to the GS550 four, but there's only an indirect link with the smaller bike. Suzuki has launched a chain-drive GS650E in America, due to appear in Europe later this year, whose engine is undoubtedly an overbored GS550. It's got 62mm diameter pistons that, with the 55.8mm-stroke roller bearing crankshaft, take the capacity up to 673cc. The top end above the crankcases is new with larger valves and a new combustion chamber. Surprisingly, the GS650E doesn't use Suzuki's Twin Swirl Combustion Chambers, in this case opting for a modified version of the two-valve set-up of the GS550 but with a more compact combustion space that allows a higher 9.4:1 compression ratio with lower domed piston crowns.

That same top end is used on the shaft-drive models that are appearing here in Britain, but with a completely new set of crankcases and transmission. The 650 shafts are different from the 6¼  pint sump, which, incidentally, also supplies the transmission and front bevel gears. Primary drive is by the familiar helical gears straight off the crank to the clutch drum and the gearbox is a five-speeder. But this is where interest lies. For Suzuki has incorporated a direct-drive top gear that's intended to reduce transmission losses and minimise slack in the drive.

Unlike the GS850G and GS1000G shaft drive models, in which the drive runs from the clutch by a quill shaft inside the gearbox mainshaft to a sprung-loaded shock absorber on the left-hand side, and thence back into the combined ignition and steering taken off the layshaft's left end, the GS650G's transmission is much more compact. Taking advantage of the 650's smaller overall size, the drive is taken back from the layshaft to the mainshaft; the final drive bevels are on this shaft, making the engine much shorter. It's a novel arrangement that not only makes the enigne more compact but also allows top gear to be direct, without running through the layshaft. Suzuki claims it cuts fuel consumption but we'll wait for the test bike to confirm that. The rest of the shaft drive is similar to, but smaller than, the GS850G's.

Overall drive ratio are identical on both the highly-tuned Katana model and the GT. Maximum power of the Katana is the same as claimed by Yamaha for its XJ650 -- 73bhp — developed in the Suzuki's case at 9,500rpm. This is eight ponies more than the softer GS650GT's 65bhp at 9,000rpm and is a result of using longer duration inlet timing and larger exhaust pipes. It also gives a higher maximum torque of42.21b-ft, compared to 48.51b-ft, but still at a rather high 8,000 rpm. Carburation in both cases is handled by a quartet of 32mm-choke constant-velocity Mikuni instruments and ignition is by magnetically-triggered coils with counterweight advancing for the timing.

Top gear for th Katana gives 126mph at 9,500rpm, a speed unlikely to be reached flat out if the XJ Yamaha is any guide, though 125mph might be possible. Maximum power in top for the GS650GT comes in at 120mph. Acceleration should be in the low 13s through the quarter mile, since the bikes weight 4731b and 4801b for Amazing what a bit of paint can do.the G and GT respectively, heavier than the Yamaha by almost 351b.

Both models utilise the same duplex cradle frame. The difference in riding position on the Katana comes from a longer stretch to the bars rear-set footrests. The Katana's pillion rests are mounted on their own tubular bracket, whereas the GT has a large rubber-mounted alloy plate which also carries the rear brake pedal. Wheels and brakes are also duplicated, the twin front differences, you appreciate the marvellous illusion — the Katana looks lighter and leaner, even though it's actually heavier. Apart from the tank, seat/side panels which are almost organic in shape, the illusion is enhanced by the black/chrome (not paint) exhaust system, the black rear half of the front mudguard and most of all the white (instead of gold-painted) wheels.

The most significant aspect of the 650s is that they provide practically the same performance as the first GS-750 four, yet they are lighter and smaller, despite having shaft drive. Even more important is that the prices — £1525 for the GS650GT and £1595 for the GS650G Katana — are almost the same as for the GS750 when it was superceded by the GSX750E at the beginning of 1980. Should you be so inclined as to insist on a chain-drive Katana model this year, there's the GS550M, which uses the same GS550 engine as the 1980GS550E. There'll also be a Katana GSX750 similar to the GSX1100S. Suzuki's sharp new blades look like they'll be everywhere this year.

Source Which Bike 1981