Skip to content
HOME » VINTAGE BIKES & MOTORCYCLE HISTORY » Whispering Giant : Kawasaki KZ1300

Whispering Giant : Kawasaki KZ1300

Kawasaki KZ1300 riding shot

I’m sitting in the road aiming my Nikon at “Redboot” Bob Duncan’s KZ1300 as it rolls toward me. I’ve done this lots of times, but the bikes are rarely this imposing. The big beast bears down on me with the presence of a Mack truck, its six header pipes like shark’s teeth, and I take a deep breath as Bob swings across the road in front of me. Next time, I’ll use a longer lens.

The seventies were an era of extravagant engineering. Having pretty much sunk the European industry and its ageing engine designs, Japanese manufacturers went on a spree of technical innovation fired, it seemed, by nothing more than exuberance. They built complex, sophisticated machinery because they could. Kawasaki introduced double overhead camshafts with the Z1; Yamaha followed with its shaft drive triples; Honda stunned everyone with its liquid-cooled, flat-four GL1000; Suzuki gave us the RE-5 rotary.

As early as 1973, Kawasaki’s engineers were working on a bike for the eighties, and in the back of their minds must have been Benelli’s six-cylinder 750 Sei of 1974. It’s almost certain, too, as their 1978 launch date approached, that they knew Honda also had a six on the drawing board. They figured that, whatever else motorcycles might become, performance would still be in fashion. In those days, that meant bigger capacity, and without carbon fibre and finite element analysis, that meant lots of metal, and therefore weight. It was go big or go home.

Inside the KZ1300 motor are more moving parts than most car powertrains. The single, plain bearing crankshaft runs on seven mains, and carries the alternator at one end and a car-type harmonic balancer at the other. It drives a jackshaft at three-quarter speed through a 33.6mm Morse Hy-Vo chain, which in turn drives the clutch/gearbox input shaft via a second, 40mm Hy-Vo chain. 

The jackshaft drives the overhead camshafts (another Hy-Vo chain of 9.3mm) and a second shaft that spins the water pump and ignition transducer. At the back of the five-speed gearbox, bevel gears turn the drive through 90 degrees to mate with the shaft drive to the rear wheel. Along the way, four dampers attempt to smooth power delivery: two spring-ramp couplers, one on the jackshaft and another on the output shaft; a rubber cush damper in the clutch; and another in the rear end.

The 130-kg power unit is housed in a suitably beefy double cradle steel tube frame with generous gusseting and reinforcing. At the front are large diameter (for the time) 41mm forks, all slowed by triple disc brakes.

The engine offers clues to its designers’ thinking. First, the undersquare cylinder dimensions of 62mm by 71mm suggest the stroke may have been increased late in development to boost capacity from a “square” swept volume of around 1100cc. Liquid cooling was almost certainly chosen to maintain a more compact overall size. With its six intake ports fed by three twin-choke Mikuni carburetors and cam profiles similar to the Z1000, the KZ produced around 120 hp and a huge 85 ft/lbs. torque but in a manner that was described as “understressed,” a clue to its future role as a touring powerplant.

ONE MAGAZINE TESTING THE KZ1300A1 IN LATE 1978 NOTED some weaving and understeer in sharp
breaking turns, and also that plenty of metal undercarriage would touch down well before cornering limits were approached. But the testers also praised its suspension and brakes, the former being air-assisted and compression damped to prevent over-compression, and the latter having drilled discs that offered superior wet weather performance.

It was noted, “the 1300’s engine is its message,” and other considerations paled. Recorded was an 11.96 standing quarter-mile with a terminal speed of 183.92 kmh—not quite as fast as the 1979 CBX. More to the point, though, the KZ1300 was run flat-out at an indicated 225 kmh for “mile after mile” with no sign of distress or instability. 

The testers’ conclusion? While agreeing the KZ would probably not meet the needs of “traditionalists” and “classical romantics,” they thought, “touring functionalists will consider what the bike can do and conclude that it is a mighty piece of work indeed … boy, can it ever get the job done.”

close-up of KZ1300 motorCOMPARISONS WITH THE HONDA CBX, LAUNCHED ALMOST concurrently in late 1978, are inevitable. In number terms, the CBX weighs around 270 kg against the KZ’s 320. The KZ’s engine is also 4cm wider than the CBX, in spite of the more compact cylinder layout possible with liquid cooling (Honda mounted the alternator behind the engine).

But they’re very different animals. The sporty CBX was the product of a single visionary, Shoichiro Irimajiri who also designed Honda’s six-cylinder race bikes, and its goal was to emphasize Honda’s technical capabilities. The KZ1300, by comparison, bears the hallmark of a committee: though perfectly competent, it seems unnecessarily complex, as though many features were Band-Aid solutions to problems that arose during development (which took five years compared with the CBX’s two). 

Given that the performance of the two machines is similar, they could be said to represent two different design philosophies: the KZ uses brute strength to propel its much more complex and heavier bulk, while the Honda relies on sophistication and aesthetically, too, the KZ is challenging: Even today, it’s a big motorcycle (so imagine—or remember—how it compared with a 1979 Ducati Supersport!) with a motor that looks like it belongs in a boat, and a vast radiator that brutally mars the lines of the frame and exhaust. 

Oddly, though, time has caught up with the KZ1300: 320 kg is no longer considered excessive, and 225 kmh performance is still respectable. It’s styling may not be du jour, but it has the timeless stance of a street standard; a rather handsome one, too.  

by Robert Smith Canadian Biker #251


Keep independent motorcycle journalism alive! If you found this article interesting or useful, please consider sharing.