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.