The Uni-Trak CPz550 really set
the middleweight class alight when it came out in 1982. It was the result of
steady development that produced a mid-weight that could give the big boys a
good run for their money.
They had it pretty much their own
way since Honda's CBX550 wasn't out and Suzuki admirable 550 wasn't out and
Suzuki's admirable 550 was not aimed at such a sports market.
Obviously the GPZ600R has largely
replaced it, but the 550 still has plenty of fans who prefer its handling,
lines and air-cooled integrity.
Power went up from 54 to a
claimed 65bhp, so the move to monoshock was a sensible and successful one. A
steady stream of improvements in every department shows what can be done
when the manufacturer sticks with one design and refines it rather than
chucking it all away and starting with a new configuration.
Like a lot of the classics here,
it is a blend of many attributes that makes it so good just as much as
outright performance.
Models and Years
The GPz evolved from the 500 in
1980, becoming the Z550A1. The basic engine configuration remained the same
throughout with double overhead camshafts running off a central chain.
58 x 52.4mm bore and stroke,
producing 54bhp at 8500rpm. This model had seven-spoke cast wheels and a
slab-sided tank, with black engine and chrome exhaust
A Z550C custom version did appear
but we'd rather not talk about it
In '81 they got closer with the
Z550GP, still with twin shocks but with 58bhp at 9000rpm, a handlebar
fairing and an oil cooler. The engine and exhaust were painted in black, but
it usually fell off when you switched on the ignition. The problem with this
model is that the power was starting to overcome the handling.
The logical progression was the
true GPz550 of 1982 with Uni-Trak rear end. Wheelbase and rear wheel travel
both went up, and the forks got air assistance and dual rate springs.
They squeezed another 3bhp out of
it with 28mm instead of 25mm inlet ports and Tekei carbs up to 26mm. Finish
was better, and you can identify this one by the five-spoke wheels and black
tail-light, it had the sidestand cut-out switch, and camchain problems were
solved by fitting a Hy-Vo chain with Teflon-coated slippers.
The final model came in 1984.
This had the LCD unit set in the petrol tank, the three-spoke wheels and a
frame-mounted fairing. Suspension was made easier to adjust and anti-dive
went on the forks. By now they had got the hang of black chrome as well.
Faults and Quirks
Despite their eventual fairly
high state of tune the CPzs don't seem either fragile or thirsty.
Pre-Hy-Vo chained models could
lunch their camchains in only 10,000 miles, but the later versions would go
on for much longer.
You can forget the ignition
except for an occasional lubing of the mechanical advance.
The later models managed to get
more performance and more economy by dint of the lean-bum engines, but these
run very hot even with the oil-coolers, so make sure you change the oil
often and keep it topped up since they hate running low.
They normally start to smoke
around the 35,000 mile mark, but can normally go on to 50,000 before you
need a top-end overhaul, which is normally for worn valve guides and piston
rings.
A major area to inspect is the
Uni-Trak rising-rate linkages, if you are going for a later model. These
have a highly stressed linkage arrangement and it needs frequent
lubrication, stuck, as it is, down where grit and salt can attack it To
check it stand at the back of the bike and lift it up and down. If it is
worn you will hear a clunking when you change direction. The handling will
be very rough and choppy. Note that there need not be any lateral movement
as the swing arm pivot may be unaffected.
Subtle refinement has made this GPz the best in its four-year history. Is it
enough to stave off the competition?
It has always been a sore point with evolutionists that the roughest
corn pone duffer can poke big holes in their theorizing with the simple
observation that you can't get Gucci from a Nauga's backside, no matter how long
you're willing to wait. Given plenty of time, a fin may sprout a toe and a toe a
Florsheim, but the leap to a whole new system is beyond the capacity of random
chance. Moving forward, according to Darwin, means moving in a series of
discrete, progressive stages.
Kawasaki understands. Since the sporting cousin of the KZ550 first appeared
on the scene in 1981, the GPz has enjoyed remarkable staying power, fending off
the onslaughts of other motorcycles through the continual upgrading of its solid
basic design. Chassis components have been modernized and refined, and every
season Kawasaki engineers wring a few more ergs from the 553cc two-valve engine
with hot-rod trickery and time-tested tuner's legerdemain.
This year's 550 arrives at the middleweight skirmish dressed in Kawasaki's
new-style "wraparound" bodywork, bringing it into fashion with the other ZX
models in the GPz corps: the 1100, 750 and 750 Turbo. A plastic, frame-mounted
quarter fairing supporting mirrors, turn signals and an inner liner replaces the
bikini screen of past GPz550s, the tank is reshaped to mesh with the sculpted
side panels, and the stepped seat has been thinned and narrowed to enhance the
bike's aggressively sporting ergonomics. The new instrumentation includes a
150-mph speedometer with push-button reset odometer, smaller-diameter tach with
integrated voltage meter, the standard cluster of idiot lights surrounding the
ignition switch, and a pod on the fuel tank displaying fuel level and a number
of warning indicators in two-color LCDs.
The GPz's new layout offers both benefits and drawbacks. First the bad news:
The short-stemmed mirrors are mounted too close to the bike's cen-terline to
offer an unobstructed view of the road behind, and the small-sized tachometer is
sometimes difficult to read, as are the warning lights in the tank pod, being
situated below the rider's line of sight. Perhaps the worst aspect of the ZX
styling is the bike's new seat. GPzs have never been renowned for their plush
passage, but the '84 550's saddle is a real pelvis cleaver—thin, stiff and
sufficiently narrow and convex that an hour's ride leaves you feeling like a
dressage competitor stuck on a sway-backed burro. On the positive side, the
rear-set footpegs and forward-mounted, narrow handlebars give the GPz more
riding room for larger riders, and the frame-mounted fairing affords good wind
protection for the upper body without compromising highspeed stability.
Modest stoking in the engine bay has upped maximum output to a claimed 65
horsepower at 10,500 rpm, five horsepower and 1000 rpm up on last year's 550.
Much of the increase comes from intake and exhaust cams with 10 degrees more
duration, fed by constant-velocity TK carburetors, one millimeter larger this
year at 27mm. The mechanical advance mechanism has been replaced by an
all-electronic
ignition system with
five degrees more spark advance near redline. The GPz's added muscle appears
when riding in its upper register, and the 550's mid-range is noticeably
stronger as well. The new GPz, far from acting high-strung and temperamental,
starts readily, warms up quickly and pulls cleanly and smoothly through the
range with no discernible hiccups or flat spots in its power curve. Fuel economy
also proved excellent for any middleweight, sport bike or no, the GPz turning in
a 46.9-mpg average, dipping to 38 mpg on one redline-intensive canyon ride.
Our GPz, a California-only model, arrived equipped with its mandated tangle
of paraphernalia for trapping evaporative emissions: a collector bottle under
the right side panel to gather condensed fuel droplets from the tank, plus a
charcoal canister mounted in the tail section, all connected by yards of rubber
hose coiling in and out around the chassis. Kawasaki representatives assure us
that performance of the California model is on a par with that of the so-called
49-state bikes; however, West Coast GPz owners are advised that accidentally
pinching the fuel fume hoses may damage the ventless gas tank when a full load
of fuel presses against the tank under heat expansion.
The greatest boon to the rider with touring on his mind is the GPz's
incorporation of the ZX series' rubber-mounting system, which isolates the
engine in a set of four elastic dampers to quell vibration. Last year's bike
with a solid-mounted engine proved an-noyingly buzzy when ridden above 6000 rpm
for anything longer than a sprint. Aboard the new 550, an irritating hum still
buzzes through the bars
at precisely 60 miles an hour in sixth gear, but this must be attributed to a
maverick harmonic; at virtually every other speed and rpm, the rubber-cradled
GPz is remarkably smooth and vibration-free.
While styling and engine alterations are the most obvious changes to the '84
GPz, much of the new model's face-lift is centered in its chassis. Here changes
abound, though it takes a keen eye to ferret them out. In an effort to keep pace
with the new breed of sporting middleweights with 16-inch front wheels, Kawasaki
has quickened up the GPz's steering geometry. The switch from a leading-axle
fork to center-axle legs steepens rake by 1.5 degrees and shortens trail by more
than half an inch. Stiffer spring rates give a tauter ride, and new-style
18-inch wheels fitted fore and aft replace last year's 19-inch front and 18-inch
rear spinners. Though the new GPz still loses ground through tight transition
turns to Suzuki's hyper-fast GS550 and the new Honda 500 Interceptor, its
newfound agility, excellent ground clearance and high-spee ahead of last year's
GPz in overall sporting prowess.
The new fork also carries anti-dive units adjusted by cranking a knurled knob
at the bottom of the fork leg. Activated by increased hydraulic pressure when
the brakes are applied, the hardware added little to fast-riding control. Unlike
many other hydraulic systems, however, the units do not compromise braking
action by creating a spongy sensation at the lever. Stopping action is linear
and progressive front and rear on the GPz, though the Kawasaki's dual front
discs cannot match the power and controllability of the dual-piston calipers
mounted on the Suzuki or the Honda 500 Interceptor.
Like the other ZX models in the GPz line, the 550's Uni-Trak rear suspension
system's gas-charged Kayaba damper is now carried in forged aluminum arms, and
the shock bolts directly to the frame at its upper end, allowing the rocker arm
and linkage to be positioned beneath the extruded, box-section aluminum swing
arm for a lower center of gravity. Wheel travel is somewhat reduced by this
system, spring rates are up, but the suppleness and load-handling range of the
GPz's new rear end give it compliance and stability to match that of the latest
ad weaponry. Damping rates are se-jcted by turning a wheel at the base of the
shock body, and preload changes are eased by the use of a remote hydraulic
adjuster mounted just under the left side panel.
If you're getting the impression the new GPz is in every fundamental way "
better motorcycle than its predecessors, you're right. Deft and careful ands
have corrected this bike's ortcomings while preserving the strengths that have
fostered a cult of GPz fanatics, and the precepts of function have been followed
at every turn.
For years, riding a GPz was as close as you could get to owning a piece of
the sport-bike rock. The 550 ruled as uncontested king of the middleweight
jungle, winning its spurs in canyon battle, often against larger foe. Now the
GPz's toughest challenge comes from its rivals in the middleweight camp; the
GS550 is quicker, the FJ600 stronger, the 500 Interceptor more advanced.
Designs have inherent limitations, and refinement risks annihilation in a
period of exploding change. Ultimately, the only law the sport-bike community
observes is survival of the fittest, and the fittest is the fastest in a world
the GPz550 did much to create.
