Motorcycle Classics

Double-Nickel Rocket: 1981 Kawasaki GPz550

1981 Kawasaki GPz550
Claimed power: 54hp@ 10,000rpm (period test)
Top speed: 119mpg (period test)
Engine: 553cc air-cooled DOHC inline four, 58mm x 52.4mm bore and stroke, 10:1 compression ratio
Weight (wet): 464lb (210.5kg)
MPG/Fuel capacity: 45-60mpg/3.8gal (15ltr)
Price then/now: $2,599/$700-$2,500

It’s a beautiful Sunday morning in late spring, a wonderful day to be riding your trusty two-wheeler down your favorite road. You’re about to lean into the best line around the next turn when a low hum announces a rider coming up behind you. In the blink of an eye he shoots past you, disappearing around the next bend. He’s gone, and somehow, the beautiful morning isn’t quite as beautiful any more.

Most of us know, or have known, a Racer Roy. Maybe you were, or still are, that envied SOB in scuffed leathers and duct taped boots who danced through back road corners like Eddie Lawson or Kevin Schwantz. And if you were a Racer Roy in the early 1980s, chances are good you were doing your canyon carving — or wishing you were — on a bright red and black Kawasaki GPz550.

Getting up to speed

Kawasaki’s first 4-stroke was the 1972 Z1, a sport-touring machine powered by a 900cc dual overhead-cam engine. It made serious waves, but as the Seventies wore on, each year’s version of the Z1 became less and less sporting. Kawasaki, like the rest of the Japanese motorcycle manufacturers, was convinced that the average American rider liked cruisers and “custom” machines, and they built what they thought their public wanted.

The Racer Roys of the 1970s bought used bikes and worked them over until they ran fast and handled well. But having to be a reasonably good mechanic and “in the loop” as to what worked and what didn’t left a lot of people out of the “racing” game. Even the guys who were good at wrenching often wished that they could be working on their cornering technique rather than a gearbox.

Someone at Kawasaki noticed that Yamaha was selling a lot of RD350s, and BMW and Ducati were getting good notice with their sport twins. In 1980, Kawasaki put a toe in the high performance waters with the KZ550 and KZ750, both inline fours with a stiff chassis and a strong engine. The 550 version in particular was light, quick and responsive.

Both displacements were unexpectedly popular: Dealers sold out immediately and started taking deposits for more. Many racetracks advertised a Box Stock class, and the Racer Roys, celebrating their freedom from 2 a.m. carburetor rebuilding sessions, quickly populated the first three rows of the Box Stock class starting line with Kawasaki KZ550s.

About the same time, Yamaha turned up with the Seca 550. Good sales and the prospect of competition inspired Kawasaki to improve on the KZ, whose brakes, forks and rear shocks weren’t up to the standard set by its engine and chassis. For 1981, Kawasaki brought out a new version of the KZ, the GPz, in 550cc and 1,100cc displacements. Cruiser-weary enthusiasts responded with enthusiasm: Here was a real sport bike.

Powering the 550cc version was an over-square 58mm x 52.4mm bore and stroke double overhead cam inline four, painted black for both improved heat dissipation and menacing looks. As an added plus, an oil cooler helped with both heat dissipation and the racy look. The compression ratio was raised to 10:1 from the previous KZ’s 9.5:1, and the chain-driven overhead cams received increases in both lift and duration. The valves were the same as before, with shim-under-bucket adjustment. Luckily, like the rest of the engine, the valves seldom needed adjustment.

And it goes …

Contemporary magazine testers praised the GPz’s well-spaced gear ratios, the precise operation of its 6-speed box and the easy operation of the clutch. One interesting feature was the neutral finder: the gearbox was designed so it was not possible to shift into second from first gear unless the bike was rolling. If the bike was stationary it would just shift from neutral to first and back.

The electronic ignition was new for 1981, and so were the triple disc brakes, rearsets, bikini fairing, air forks and adjustable-rebound rear shocks. Air-charged forks and adjustable shocks were not common items in 1981, and the prospect of not having to discard the stock suspension in favor of aftermarket improvements helped GPzs fly out dealers’ doors. Racer Roys appreciated how the GPz pulled out of low speed corners, with a wide powerband and ample acceleration.

The bright red tank, fairing and fenders inspired one contemporary magazine to print a public service announcement: The Kawasaki would not only be quickly noticed by fellow riders and patrons of the local motorcycle gathering spot, it would also be quickly noticed by the Highway Patrol.

Contemporary testers agreed that the Kawasaki GPz550 had one glaring fault: It took forever to reach operating temperature. As owner Zeki Abed explains it: “It takes a day and a half to warm up. You can start the bike and go get a cappuccino and a bagel with cream cheese before it warms up. Then — and only then — can you drop the choke all the way and it will idle.”

Once (finally) warmed up, the GPz became a tractable road machine, easy to maneuver through crowded city streets. The combination of a relatively short wheelbase, relatively light weight (469 pounds with a full tank of gas) a stable chassis and good brakes made for a nice combination of agility and stability.

While testers agreed the GPz was a good city bike, they also agreed that the fun really started when the city limits were left behind for the nearest hills. The engine liked to rev, peaking at just more than 54 horsepower at 10,000rpm in a 1981 Cycle test (Kawasaki claimed 57 horsepower at 9,500rpm). The bike turned quickly, but maintained a predictable line through tight turns, making the GPz an excellent platform for the Racer Roys of the world. “At the time, a GPz was the mark of the back road racer,” Zeki says.

Further developments

As the GPz roared out of showrooms, shortages developed shortly after the bike was introduced. Many quickly reappeared at the local track, replacing the KZs of the year before. The success of the GPz spawned rivals: Suzuki came up with the GS550M and Yamaha continued its development of the Seca and introduced the Vision.

For 1982 Kawasaki, working to stay ahead of the pack, continued its program of chassis development and equipped the GPz with a monoshock rear. The bottom of the shock mounted to the swingarm, while a bell crank connected the top of the shock to the frame and the top of the triangulated swingarm. This rising rate system was not steadily progressive: a soft initial ride jumped to increasing stiffness at the beginning of compression and became really hard near the end. The GPz’s shock featured both adjustable rebound damping and adjustable spring preload. The monoshock stretched the frame out 2 inches.

At this point, Kawasaki decided to sit on its middleweight laurels and stopped making major changes, although continuing minor refinements have led many owners to feel the 1983 version is the best-handling of the GPz550s.

The decision to slow the development of the GPz may have been precipitated by economic conditions in the U.S. Due to widespread unemployment in the early Eighties, motorcycle sales were dropping like a rock. Plus, Honda and Yamaha had started a trade war that ended in huge surpluses of bikes sitting on showroom floors, eroding prices. An additional factor was the decision of Kawasaki to develop a new, water-cooled engine for its sport bike line.

Yet despite the bad American economy, and even without substantial upgrades, the Kawasaki GPz550 sold. It was more versatile than many other two wheelers claiming the title of sport bike, and while not really adequate for long-distance touring, the light, fast and easy-to-ride GPz would happily take its owner to work or school, day after day, its engine praised as “reliable as a claw hammer.”

In 1984, the GPz was restyled with a larger fairing. The era of All Red, All the Time, was over: The 550 was now available in silver, with broad red and blue stripes. The engine was tweaked and the rear suspension was revised.

In 1985, Kawasaki rolled out the liquid-cooled engine its engineers had been developing, bolted it to a completely new frame with new geometry, and named it Ninja. The GPz hung around for another year, and then retired.

Keeping them around

Although the Racer Roys of America had long gone on to Honda Interceptors and FJ Yamahas, a lot of people hung on to their GPzs for commuting on weekdays and fun on weekends. Unlike the more specialized sport bikes, the GPz was more than just a canyon-carving weapon. “Kawasaki’s GPz offers the best ergonomics, the best freeway ride, the smoothest motor and the most seamless carburetion,” Cycle Guide said in 1984. The reliable drivetrain added to owner appreciation.

Recently, GPz550s have taken on a new role: collector’s item. Some of the Racer Roys of the 1980s have grown nostalgic, and others have found renewed appreciation for a bike that was both easy to ride and to maintain. Zeki explains: “Back when I was growing up, a GPz was the mark of the back roads racer. I didn’t have one, and I envied the guys who did. It was a significant advance in technology available to the general public. Over the years, I have owned a lot of 1982s and 1983s, but what I really wanted was the 1981 model, with the dual shocks. THAT was an old school fast bike.”

Kawasaki never expected the first GPz to sell like it did, and didn’t produce very many that first year. “Finding a 1981 model is not easy — it’s a rarer bike,” Zeki says. “This one was found deep in the heart of Texas, original and unrestored. It even had the original mirrors. I paid top dollar for it.”

This low-mileage bike needed no engine work and little else besides careful detailing. The gauges look brand new. Used bike consumer guides caution that the GPz’s exhaust will rot out quickly, and the one item Zeki had to replace was the original mufflers, swapping out a set from a second bike he owns. But all of the GPzs Zeki has owned, including this one, have been as reliable as they are claimed to be. “There’s virtually no maintenance; it’s like a Toyota Corolla — put oil in it and it runs.” Although used bike guides note the top end, electronic ignition and cam chain may go out after 50,000 miles and engines wear out after 80,000 miles, Zeki thinks otherwise. “You can’t break that engine,” Zeki says. “You may get oil leaks, but that’s it.”

Although the GPz is no longer state of the art, it is still easy to ride, fast or slow. Zeki rides this bike through the canyons around his home, and he suggests that a GPz is ideal for a new rider looking for an upgrade from a 125cc or 250cc first bike. “It’s bulletproof and light, with an excellent riding position,” he says. Seasoned riders will also like this bike. “Once it’s warmed up, it’s pure bliss, sewing machine smooth. It’s flickable, tractable and sane.”

Compared to today’s sport bikes, it is slow, but the brakes work well — those triple discs were amazing back in the day. And it has all the sport bike icons. Oil cooler? Check. Sexy bikini fairing? Check. Mag wheels? Check. Air adjustable shocks? Check.

The Kawasaki GPz550 set the standard for the middleweight sport class of the early 1980s. It was the mark to meet or beat, and it was a bike the Racer Roys were happy to explore — then, and maybe still today. MC

  • Published on Oct 5, 2012
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