The Kawasaki GPz750 makes a good case for simplicity and straightforward engineering. Wayne Rainey used a race-bike based on the stock GPz to win the 1983 Superbike Championship even though, on paper, the Kawasaki shouldn't have been competitive with the Honda V-Fours ridden by Raineys' main competition. That Rainey won is a tribute both to his hard riding and the engine building ability of Rob and Steve Johnson and the rest of the Kawasaki race crew, but it's also a tribute to the motorcycle used as the basis for Rainey's racer.
That tribute is reinforced by a little-expected fact: in California, in New England, in the South, GPz750s are winning stock-class club road races and defeating Honda VF750F Interceptors in the process, all the while remaining reliable and trouble free.
The GPz750 for 1984 is still 738CC with bore and stroke of 66x54mm. The dual camshafts ride directly in the cylinder head casting and act on bucket tappets set over each valve and spring, and lash is adjusted by replacing small shims positioned in the top of the valve spring retainer, beneath the tappet bucket. The cams are driven off the center of the plain-bearing crankshaft by a link-plate chain. Another, wider link-plate chain carries power from the crank to output shaft, which drives the wet, multi-plate clutch through a gearset. The transmission has live speeds and final drive is a 630 O-ring chain.
The GPz breathes through a set of four 34mm Mikuni CV carbs; the exhaust system is black chrome; and the ignition system is electronic.
The dual-downtube steel frame uses a single (damping and air pressure adjustable) rear shock connected to the aluminum swing arm by a system of progressive linkages. Wheelbase is 58.9 inch., rake and trail 28 degrees and 4.6 inch. The drive chain is adjusted by moving the rear axle back in a pair of concentrics.
If all that sounds familiar, it is: The 1984 GPz750 is essentially the same as the 1983 GPz750. There are a few changes: GPz750s are available in silver paint or the traditional bright red; the 18-in. cast alloy wheels are painted grey with polished highlights instead of red with polished highlights; the frame-mounted fairing has a smooth inner liner; the drive chain is lighter thanks to holes drilled in the inner link plates, and longer-lasting thanks to new silicone grease used inside the O-ring sealed rollers.
The handlebar change alone improves riding comfort dramatically, and now the GPz750 isn't comfortable only at twice-legal speeds. In fact, the new seating position created by the bars changes the personality and feel of the bike around town and on the highway. Without the distraction of aching wrists and shoulders caused by the 1983 bars, the rider notices how good the Kawasaki's suspension is. In normal use, the Kawasaki is a comfortable motorcycle.
The bike has good top speed, too, although reaching that speed takes more than a half-mile: our 1984 test bike reached 123 mph in the measured half-mile, down two mph from 1983. But given enough room, the Kawasaki will redline fifth gear, reaching 136 mph.
The Kawasaki's best quarter-mile time on a less-than-perfect day was 12.43 sec. with a terminal speed of 106.25 mph, slower than our 1983 test bike's 12.13 sec. at 109.48 mph. The Kawasaki makes good peak power, a claimed 85 bhp at 9600 rpm, but the power band has a big bulge above 7500 rpm and lacks the mid-range power of the Suzuki or Honda 750s. The power distribution is most apparent coming off stoplights or pulling around slower traffic on the highway; a fast launch takes a lot of rpm, and a fast pass takes a downshift or two depending upon the initial cruising speed. The GPz turns 4400 rpm at an actual 60 mph (indicated 60 is an actual 55 mph).
At that speed—and at every other engine speed—the Kawasaki is the smoothest 750 on the road, thanks to rubber front engine mounts. There's no resonance in the bodywork, no buzzing grips, no blurred images in the fairing-mount rearview mirrors (although those mirrors do show too much elbow and sleeve and not enough roadway-to-the-rear).
The Kawasaki's gauges are a combination of simple and -tech, conventional and unusual. The speedometer is straightforward, reading to 150 mph with built-in odometer and resettable trip meter. The tachometer is smaller, perhaps two-thirds the size of the speedometer, and doubles as a voltmeter if the rider pushes and holds down a button on the instrument mount panel. Flanking the upper-triple-clamp-mounted ignition and fork lock switch are small pods containing warning lights for turn signals, high beam, neutral, and headlight failure. There's also a red light that flashes if the fuel or battery fluid level is low, if oil pressure drops or if the sidestand is down. To see which problem the light refers to, the rider must look down at an LCD display panel mounted on the top of the gas tank, ahead of the gas cap. The fuel gauge is a sort of bar graph - the more bars show, the more fuel there is in the tank. The split location of the gauges and the instruments isn't universally popular - some riders hated it.
Where our test Kawasaki shone was in braking. It needed just 119 ft. to stop from 60 mph with perfect control and excellent feedback through the firm handlebar lever. The anti-dive system, which increases compression damping to slow fork compression under braking, is controlled by a valve activated by brake fluid pressure. The system is adjustable, with four settings selected with a plastic knob on each fork leg, but even at the firmest setting the system has no noticeable effect. That obviously didn't hurt the braking.
The Kawasaki's Dunlop tires - a 110/90-18 F17 front and a 130/80-18 K427rear - are among the best original equipment tires and work well with the responsive brakes. They're fine for vigorous street riding as well, holding well and delivering good tread mileage too.
Astute readers will no doubt remember that when we compared the 1983 Honda, Kawasaki and Suzuki 750s, the Kawasaki came in third in just about every measure of performance. The test didn't show the Kawasaki's long-term durability and response to easily-performed, class-legal modifications.
It seems that adding five or six teeth to a GPz750's rear sprocket, a good valve job, second-oversize Kawasaki pistons and strict attention to minimum factory specifications for cylinder deck height all work wonders for a Kawasaki. The fact that the Kawasaki is easy to work on encourages its modification, unlike the Honda and its cast-into-the-crankcase cylinders.
So it is that a two-valves-per-cylinder, air-cooled GPz is able to run with and defeat a four-valves-per-cylinder, water-cooled VF750F and a four-valves-per-cylinder, air-cooled GS750 on the road race track.
Compared with the rest of the class, then, the Kawasaki is geared tall, which hurts dragstrip and roadrace performance (at least until the sprockets are changed by the owner) but helps mileage. On our mileage test loop, the Kawasaki returned 52 mpg.
Which brings us to a small disclaimer. The machine seen and tested here is a 49-state model. Bikes brought into California in 1984 must have a charcoal cannister system for capturing unburned hydrocarbons vented from the gas tank and carburetors. Kawasaki positions its cannisters in the tail section and routes hoses from the carbs and tank vent to the cannister. The entire system adds a pound or two to the bike's weight, Kawasaki representatives tell us, and doesn't affect performance. But our test bike wasn't fitted with a cannister.
As delivered, Kawasaki's GPz750 isn't as fast nor as quick as a Suzuki or Honda 750, but riders who don't race and don't ride Suzukis and Hondas back-to-back with a Kawasaki will never notice the differences in power delivery. It is smooth, reliable and responds well to minor modifications to increase power. Because it isn't the quickest and fastest 750, the GPz is discounted in many states, making it a high-flash bargain. But discounted or not, the GPz750 is capable of giving its rider a lot of trouble-free fun.
Source Cycle World 1984