Kawasaki GPz550

Introduced in 1981, the GPz was an upgrade of the KZ550 street bike, with a hot-rodded version of the old machine’s four-cylinder engine, an air-charged fork, adjustable shocks and a bikini fairing.

The new engine generated a claimed 57bhp at 9,500rpm, 4bhp more than the KZ’s power plant, and propelled the 469lb machine to a quarter-mile time of 12.65 seconds — a class record — in a test by Cycle World.

“750s Beware! Here Comes the GPz550,” blared the cover of Motorcyclist in February 1981.

Similar praise flowed like Cutty Sark at a Shriner convention. Reviewers found that the bike worked well on twisty roads and on longer hauls, thanks to comfortable ergonomics and 51mph highway mileage, a 3.8gal tank and a reasonably wide and supportive seat.

The GPz was hailed as a bike that could be used as a commuter during the week and raced on weekends, an all-around thrill ride that would demolish other bikes in its class and even leave most 650s in its mirrors.

Scott Pratt, owner of a 1984 Kawasaki GPz550, says the bike remains potent. He’s clocked quarter-mile times as low as 12.80 seconds on a bike virtually all stock except for a K&N air filter and a Stage 1 carb kit.

“My brother has a Ducati Monster 750, and it totally shocked him that his bike and mine run virtually identical,” Pratt says. “You could throw a blanket over us at the finish line.”

Birth of a species

Kawasaki had already produced the lightest, quickest and best-handling half-liter bike on the road with the 1980 Kawasaki KZ550, but a growing interest in pure sport bike and competition such as Yamaha’s Seca 550 spurred the creation of the GPz.

To generate more horsepower, Kawasaki engineers punched out the cylinders an extra 3mm and raised the piston dome height from 2.6mm to 4.0mm, increasing the compression ratio from 9.5:1 to 10:1. Main jets were enlarged, and the camshaft was swapped to increase lift on both the intake and exhaust valves.

A steep fork angle and a short (54.9in) wheelbase results in quick and precise steering, and cornering clearance was more than reasonable.

On the downside, the fairing didn’t do much for aerodynamics or rider protection, and the bike was widely criticized for being cold-blooded.

Still, the GPZ’s overall performance and features such as triple discs and an oil cooler drowned out the nit-picking, and it didn’t take long for waiting lists to start forming at dealerships.

A middleweight superbike class was born, and Kawasaki was king.

“If you wanted a cutting-edge 550-class sportbike anytime over the past few years, your choice was simple: You bought a GPz550,” Cycle Guide said in 1984. “Kawasaki so dominated the class that all challenges were little more than minor skirmishes along a very secure border.”

The company stayed on top through constant refinement such as a monoshock rear suspension in 1982; and a body-mounted fairing, new frame and redesigned bodywork in 1984.

Lasting impression

We suspect Kawasaki also sprinkled some sort of voodoo powder on the bikes, because they’ve cast an enduring spell on owners.

For various reasons, Goodwin went years without a good opportunity to buy a GPz. But he never lost the faith, even as someday turned into some decade.

“I kept looking, and finally I happened to find a good one on eBay. I’d had other bikes over the years, but this was the one I really wanted.”

Goodwin finally made his purchase in December 2004.

Pratt has a similar story, buying his GPz more than 20 years after he first laid eyes on one.

“I went to a dealership one day when I was going to college in Daytona, and there was an ’81 there on the floor. It was very striking in its day. It had that nice, European look to it. I started paying more attention to it after that.”

After being led away from motorcycling for several years by family and career responsibilities, Pratt was able to ease back into the sport three years ago.

“I looked at some other bikes, but the GPz was ultimately what I wanted,” he says.

Changing times

Despite its appeal and mountain of good reviews, the GPz550’s reign ended abruptly when the middleweight wars went to a new level of performance in the mid-Eighties with such bikes as the Yamaha FJ600 and the 600 Ninja.

The bike was discontinued after 1985 but has refused to go away thanks to above-average reliability and ongoing appeal to riders in their 30s and 40s.

When Corey Clough acquired his ’85 GPz550, it had more than 30,000 miles on the odometer and had been stored for four years. With minimal maintenance — a carb kit and new tires, chain and sprocket — Clough had a rock-solid commuter bike.

“People don’t realize the potential of these bikes,” he says. “If they did, they’d sell for a lot more.”

As it stands, the 550 is a bargain leader on the resale market. Presentable, low-mileage bikes can be had for less than $1,500, and higher-mileage units sell for less than $1,000.

“I knew a little about them when they came out, but then I got more interested with I started seeing them show up on a lot of best-value lists,” says Scott Hawkins, who bought an ’81 GPz550 in good condition for $700.

Goodwin attributes the 550’s low resale value to a stigma attached to half-liter bikes.

“People think that if it’s not a liter bike, it’s not a man’s bike. But I’m 6-foot-1 and pushing 300lb, and my bike has plenty of power.”

Pratt says anyone who sniffs at the 550’s displacement is missing a bigger picture: a well-balanced combination of power, handling and reliability.

“The handling is a lot better than what most people who ride modern bikes are going to give it credit for. A lot of guys think you need fat tires, but this is not a high-powered, modern muscle bike, so it doesn’t really have a traction problem. It drops into a turn very rapidly and it has a ton of ground clearance. Plus, I’ve put about 10,000 miles on mine — including more than 150 quarter-mile runs — and it’s never let me down whatsoever.” MC