How Kawasaki’s GPz550 Changed the Course of Middleweight Sportbikes in America

The late 1970s were not a boom period for the venerable middleweight streetbike. By '79 the class had become almost passé, sniffing the tire smoke of larger and more exciting machines such as Kawasaki's KZ650 (which ran with top-line 750s) and KZ900/KZ1000 (sons of the Z1), Yamaha's smooth and fast XS Eleven shafty, Suzuki 's ultra-capable GS750 and GS1000, and Honda's scintillating, 24-valve, six-cylinder CBX.

Yamaha’s two-stroke RDs had pretty much carried the middleweight torch during the ’70s, along with nice-but-unexciting motorcycles such as Honda’s CB500/550F and Suzuki’s GT380 and 550. (Honda’s ill-fated CB400F was a cool but weak-selling exception.) But as 1979 clicked over into 1980, it was clear that 400cc two-strokes (even Yamaha’s stellar Daytona Special) had run their course, while 500 and 550cc four-stroke twins and multis stuck largely to their boring, Universal Japanese Motorcycle design. If you wanted arm-stretching, peg-dragging excitement in a Japanese motorcycle, you went open class.

But just as the Carter years morphed into the Reagan era, that boring middleweight credo was flipped upside down when, in the fall of 1980, Kawasaki announced the now legendary GPz550—a motorcycle that would alter middleweight history. The GPz550 was Japan's first real hot-rod middleweight, a glossy-red poke in the eye of everything that was boring and staid on the sporting landscape. Fast, sexy, and nimble, the GPz not only catapulted Kawasaki into the leadership position for middleweight streetbikes, but it helped forge the foundation of what would soon become Kawasaki's iconic Ninja nameplate, an epically successful brand if ever there was one.

"I remember seeing the GPz550 in Japan sometime in the fall of '79," longtime Kawasaki man Mike Vaughan says. "This was a year or so before it was announced. I was with a small group of sales and marketing guys from Kawasaki US, and I clearly remember our jaws dropping when we saw the bike. The bright-red paint. The blacked-out engine. The cockpit fairing. And the GPz name. We were stunned. It was really exciting! They'd fitted hexagonally shaped mufflers on one of the prototypes, which we didn't like, and said so. But otherwise, the thing was spot on. When the factory guys asked if we would be interested in something like this for the US market we couldn't say yes fast enough! I mean, you just could not turn something like that down."

The roots of the GPz550 (GPzs would be seen in 550, 750, 1100, and 305 iterations during the early and mid-1980s) can be traced primarily to the mighty 903cc Z1 of 1973 and the machines spun from it. As the Z1 developed during the middle-to-late 1970s, becoming the KZ900, KZ1000 and the café-flavored Z1R of 1978 (which would strongly influence GPz styling), Kawasaki also began building smaller fours with the same performance focus. These were UJMs, for sure, but very good ones. The rapid, 750-beating KZ650 of 1976 came first, followed by the highly capable KZ550 of 1980 (upon which the first GPz550 was based). The KZ550 was basically a 3mm overbore version of the Euro-spec Z500, introduced in 1978. A 400cc version, the Z400, was also produced for the Japanese market in ’78.

The KZ550 was a solid motorcycle and good sportbike, too, especially when tweaked with better suspension and tires. "Our testbike was pretty strong," former Motorcyclist Senior Editor Jeff Karr says. "I put a Dunlop K81 on in place of the ribbed front and took it to the AFM races at Ontario Motor Speedway. It won 600 Box Stock, 600 Production, and was second or third in 600 Supersport. Not a bad day of racing!" The KZ550 sold reasonably well, too, though its understated paint and styling (not to mention its single disc front brake) helped keep it from becoming the middleweight phenomenon it could have been.

With a middleweight as good as the KZ550, you’d think Kawasaki would simply refine and continue to produce it for as long as it could. In many ways that’s what Kawasaki did, though the jump in performance was huge and the resulting motorcycle was no longer called a KZ550. For 1981, this upgraded machine would be known as the KZ550GP, or more popularly the GPz550. It would soon blow the lid off the middleweight category, setting the stage for even faster and tricker 550s—and, eventually, 600s—in the coming years. The KZ550 would stay in the lineup, but the GPz would slide into Team Green’s 550-class hot-rod slot.

“As far as I can tell,” Vaughan remembers, “the whole red-and-black, cockpit-fairing GPz thing came from the Japanese side. I’m sure some of the Z1R’s aesthetics affected GPz styling…the fairing, coffin-shaped tank, black engine, et cetera. However it happened, and whoever came up with it, the GPz was a big hit visually.”

The GPz550 was a big hit dynamically too—on the street, at the dragstrip, and especially at the racetrack, where it became the middleweight to have for club-level racing. Its combination of ultra-serious looks, class-leading performance, light weight, durability, and reasonable comfort resulted in sales-number gold for Kawasaki and its dealers.

“Our store was always backordered,” says Tim Rutherford, who owns and runs Century Motorcycles in San Pedro, California. “We sold every GPz550 we got, and we could never get enough.”

“There was always a line of guys out front on Saturday mornings,” remembers Alex Arrues, who owns and runs Kon-Tiki Motorcycles in San Diego, California. “Some were there to put a deposit down, others to pick up their bikes. We never had enough GPz550s!”

“The things were everywhere,” says longtime DC-area motorcycle dealer Jack Seaver. “On the street, at the racetrack, at the strip. The GPz550 pretty much took over where the RD350 and 400 had left off: fast, light, fun, and affordable. It became the club-racer to have and dominated the middleweight division for years.”

Kawasaki got all this impressive performance by heavily tweaking the base KZ550 platform. To the KZ’s already stout, 553cc four, engineers added hotter camshafts with more duration and lift. The GPz received domed pistons for increased compression. As a whole package to increase power, Kawasaki also gave the GPz reshaped ports, electronic ignition, a less-restrictive airbox and exhaust, and larger main jets. Output jumped from a claimed 53 to 57 hp at 9,500 rpm (the redline), yet the bike retained much of its prodigious (for a middleweight) midrange power, which is so appreciated on the KZ.

The chassis got a host of upgrades, too, the biggest of which were triple discs in place of the KZ’s solo front disc/rear drum combo. Kawasaki also added a neat cockpit fairing, rearset footpegs, an air-adjustable fork, (rebound) damping-adjustable shocks, a low handlebar, a fuel gauge and oil cooler, all topped off with Firecracker Red paint and black-painted engine and wheels. And while the GPz retailed for $300 more than the KZ ($2,599 versus $2,299), you’d be hard-pressed to buy all those upgrades for three bills. All in all, the GPz550 was packed with good stuff, and everyone who cared about sporty bikes noticed.

“The Kawasaki GPz550,” we wrote in our February 1981 issue, “is the kind of motorcycle we thought we’d never see again in America. We like it not only because it packs a genuine superbike wallop but because it brings the kind of functional sense of purpose sporting riders find so appealing—and so rare. The seasoned rider who looks to twisting roads and twitching tach needles is unlikely to find a better mount—of any size—than the GPz550.”

Our “superbike wallop” characterization was apt, for the little red rocket packed amazing numbers at the strip—an astonishing 12.57-second/104-mph run in the hands of Jay “Pee Wee” Gleason (normal tester Jeff Karr was away that day). That was quicker than the legendary 500cc H1 by four-tenths, quicker than the original Z1 by a hair, quicker than the KZ550 by a half-second, quicker than the Suzuki GS550 by a full second, quicker than Yamaha’s Seca 550 by four-tenths, and about equal to Suzuki’s 16-valve GS750E. Amazing.

Cycle World agreed. In its August 1981 road test, editors finished up with this: "The GPz offers a lot of what the first Kawasaki Z1 had going for it; performance without the sacrifice of civility."

"The only thing the GPz550 lacks is a set of number plates," wrote Motorcyclist's Ken Vreeke in his "Off The Record" notes. "I was impressed with the KZ550, but the GPz is threatening my life savings. Can you imagine the grim look on the CB750 owner's face when you shut him down from the stoplight and leave him through the next series of turns? The words 'bone stock' will never be so satisfying. As far as I'm concerned, the Europeans can taunt us with whatever it is that we can't have, and it won't bother me in the least; we've got the GPz550."

Just a year later, the crushing speed of streetbike development during the early 1980s was on display when Kawasaki introduced a revised GPz550. The ’82 model featured sexy new bodywork, revised LCD instrumentation, and a single-shock rear suspension system—Uni-Trak in Kawasaki speak. That bike carried into 1983 with only paint and graphics changes, and it was more of the same on the sales floor, in the magazines, and on the racetrack.

“It really was a phenomenon,” Vaughan says. “They just continued to sell like crazy. A dealer I knew told me he’d sold 28 or 30 of the things, and 95 percent came back crashed! You knew guys were out there riding them fast—or racing them. I remember one box-stock middleweight grid at Willow Springs, a few months after we’d put up some contingency money. There were 130 bikes on it, 90 percent of them GPzs. I think they did a three-wave start!”

In 1984, Kawasaki revised the GPz550 again, introducing swoopy bodywork and a host of other engine and chassis updates. But by then things had changed in a dramatic way: liquid-cooling, 16-inch front wheels, and perimeter frames were the things. The radical new 900 Ninja was out, and in less than a year the 600 Ninja would be too. GPz out, Ninja in, and we all know the amazing transformation that occurred during the 1980s in the sportbike category for Kawasaki and the other Japanese makers.

And that Ninja name? It came, interestingly enough, from Vaughan. “I had a sailboat named Ninja,” Vaughan says. “And I thought it might work as a name for a new sportbike. I brought it up during GPz discussions, and while it was too late to use it then, everyone liked it, so we registered it for later use. And, boy, did we use it later! I’m sorta happy I brought the idea up!”

We’re all pretty happy Vaughan and his colleagues nodded their heads “yes” when asked if America wanted the GPz550. That motorcycle got everyone worked up again about middleweights. And things certainly haven’t been the same since.

In 1990 I quit as executive editor of Motorcyclist and took a job writing advertising for Acura. I was curious to see if I could hold down a real job—and live without testbikes. I found a clean '81 GPz550 with 15,000 miles. It had a lawnmower-inflicted dent in the tank, but I wanted function, not form. A cool $1,000 later she was mine.

Our time together was long on miles and short on washing. I rode it to the Laguna Seca GP with my girlfriend on the back. Even two-up, I could pace my buddies’ hot CBR600s and CBR1000s. It handled so well and I had grown so used to it that we were making up in corner speed what their liquid-cooled rockets gained on the straights.

The clock rolled from 15K to 50. The ignition switch got so loose that the key popped out if I hit a certain bump. That certain bump happened to be on my daily shortcut to work. The key popped out one morning, tumbled off the tank, and skittered into a storm drain. I bought a new switch.

A certain Mr. Boehm, with his mania for old Japanese streetbikes, inspired me to write a few checks and pay the GPz back for all the miles she had given me. The idea was to keep the OEM exhaust (I hate noise), airbox (I hate noise), and emissions plumbing (I hate smog)—while updating the engine and chassis.

I sent the bodywork and ColorRite (colorrite.com) paint to the amazing Larry Pearson, (meticulousmotorcyclepainting.com) for a finish better than new. Race Tech (racetech.com) dialed the suspension, with GS-3 shocks and Gold Valve Cartridge Emulators. I got new EBC (ebcbrakes.com) discs and pads. Sprocket Specialists (sprocketspecialists.com) sprockets and a D.I.D X-ring ERV3 chain (didchain.com), in a slimmer 520 size, shaved a couple ounces and saved a couple bucks. Dunlop GT501 tires (dunlopmotorcycle.com) promised a nice balance between durability and grip. Mike Cortez and Alex Arrues from Kon-Tiki Motorcycles (kontikimotorcycles.com) installed a Wiseco 615cc big-bore kit (wiseco.com), rebuilt the head, rebuilt the brake cylinders and calipers, screwed it all together, and retuned the jetting.

The result, for a modest $2,200 investment, was better than I remembered. Even with more than 50,000 miles on the odo, it rides like a quick NOS GPz550: low and long, with old-school, higher-effort steering and controls, but capable of hurting slightly slower riders on much faster motorcycles. The Race Tech suspension is firm but not harsh. The new brakes are wonderful—solid, strong, and predictable. The motor is smooth, flexible, and surprisingly powerful. As with many things in life, I wish I had done all this 25 years ago. — Dexter Ford