29/10/2007
Kawasaki KZ750: A Tale of Two Engines
In the annals of motorcycle history, certain model designations carry a weight of recognition, often evolving and adapting to the ever-changing landscape of rider expectations and technological advancements. The Kawasaki KZ750 is one such nameplate, a series that, perhaps surprisingly to some, encompassed more than one distinct engine configuration during its production run. While many associate the KZ series with the smooth, sophisticated inline-four engines that dominated the Japanese motorcycle scene in the late 1970s and early 1980s, Kawasaki, in its characteristic fashion, also offered a parallel twin variant of the 750cc machine. This article delves into the nuances of both the inline-four and parallel twin KZ750 models, exploring their design philosophies, performance characteristics, and their place in the broader context of motorcycle evolution.
The KZ750-E: An Evolution of the Inline-Four
The 1981 Kawasaki KZ750-E represents a direct lineage from Kawasaki's successful KZ650 four-cylinder platform. Ben Inamura, a key engineer at Kawasaki, was instrumental in the development of both the legendary Z-1 900 and the highly regarded KZ650. The KZ650, with its 652cc displacement, was designed to offer the handling of a 500cc machine with the power of a 750cc, all while being competitively priced. By 1979, however, the 750cc class had surged in popularity, prompting Inamura to consider an increase in displacement for the KZ650.
The resulting KZ750-E was not a radical redesign but rather an expansion of the existing KZ650. The cylinders were bored out from the 650's 62mm bore to a more oversquare 66mm, while retaining the 54mm stroke, resulting in a total displacement of 738cc. This placed it in direct competition with contemporaries like the Honda CB750, which featured a perfectly square 62x62mm bore and stroke for 749cc.
A notable aspect of the KZ750-E's design was its adherence to the proven two-valve cylinder heads, similar to those found on the KZ650. These heads featured shims located beneath the cam followers, necessitating the removal of the camshafts for valve gap adjustments. While this procedure was straightforward for experienced mechanics, many riders opted for professional servicing. Kawasaki did incorporate one-millimeter larger exhaust valves and introduced small anti-smog vents to meet emissions regulations. These vents allowed oxygen into the combustion chamber to burn off unexploded hydrocarbons, converting them into carbon dioxide, a more environmentally acceptable emission.
Performance and Advancements
Despite the minimalist approach to the cylinder head design, the KZ750-E did not suffer in performance. The KZ650 produced close to 50 horsepower, and the addition of nearly 90cc boosted the KZ750's output to over 60 horsepower at the rear wheel, with peak power arriving at a brisk 9,500 rpm. These figures were impressive for the era and contributed to the bike's appeal.
Key upgrades from the KZ650 included the adoption of 34mm Keihin constant-velocity carburetors, replacing the smaller units on the 650, and the implementation of a transistorized ignition system. Interestingly, this new four-cylinder engine was first introduced in South Africa, a smaller market, likely as a consumer testing ground before its release in the more significant US and European markets. This strategy allowed Kawasaki to gauge the bike's durability and performance under real-world conditions before a wider launch.
The KZ750-E also featured sportier camshafts, which enhanced power delivery without compromising the torque characteristics that riders appreciated for street riding. The larger CV carbs, while contributing to the increased power, also led to a thirstier fuel consumption, with mileage dipping below 40 mpg when ridden spiritedly and even below 30 mpg when pushed hard. For riders prioritizing economy, the KZ440 twin offered a more fuel-efficient alternative.
Chassis and Running Gear
Kawasaki carried over much of the KZ650's chassis, with minor revisions to lower the saddle. The most significant updates were found in the suspension system. The front end featured an air-adjustable Kayaba fork offering nearly six inches of travel, allowing riders to fine-tune the firmness. The steering geometry, with a 27-degree rake and 4.2 inches of trail, combined with a wheelbase just under 60 inches, contributed to the motorcycle's agile and quick-turning nature.
At the rear, a pair of Kayaba shock absorbers provided tool-less preload adjustment via a large, grippable collar, a convenient feature for riders. These shocks offered four inches of axle travel. While some test riders noted the suspension as being slightly too soft for aggressive riding, Kawasaki understood that the majority of its customers prioritized comfort over the absolute limits of lean angle. Enthusiasts seeking a sportier setup could easily opt for aftermarket modifications.
Braking was handled by triple 10.2-inch discs with single-piston calipers, providing adequate stopping power for the average street rider, though racing-oriented riders might have desired more aggressive braking performance. The cast wheels were shod with Dunlop Gold Seal tires, in sizes 100/90-19 at the front and 120/90-18 at the rear.
Riding the KZ750-E was described as a comfortable experience, with a plush seat and slightly raised handlebars that encouraged a relaxed riding posture. The engine started easily, and the clutch engagement was smooth, leading to a pleasant ride. In terms of performance, the KZ750-E could achieve low 12-second quarter-mile times with a competent rider, outperforming the Honda CB750F, though the pricing of the two models had become very similar by this point.
The KZ750 Twin: A Different Approach
While the KZ750-E was an evolution of the inline-four, Kawasaki also produced a parallel twin version of the KZ750, often designated by models like the KZ750-B or KZ750-CSR. This parallel twin engine, which debuted in 1976, was a more traditional configuration, drawing inspiration from earlier parallel twins that had enjoyed popularity.
The KZ750 twin was a four-stroke parallel twin with a double-overhead-cam (DOHC) top end, a relatively modern feature for a parallel twin of its era. It also incorporated chain-driven counterbalancers to mitigate vibration, a common issue with parallel twins that could detract from rider comfort. Kawasaki aimed to improve upon the vibration issues that plagued rivals like the Yamaha XS650. While the KZ750 twin managed to reduce vibration compared to some older designs, it still exhibited noticeable shaking, particularly at higher engine speeds.
Despite its DOHC setup, the KZ750 twin featured only two valves per cylinder and produced around 55 horsepower at 7,000 rpm. In performance terms, it was generally considered less sporty than the inline-four KZ650, which produced more power and had a more engaging powerband. The KZ750 twin was often described as a "dog" in the performance department when compared to its four-cylinder sibling.
Design and Market Positioning
The KZ750 twin often sported a more retro aesthetic, similar to the Yamaha XS650, suggesting a deliberate marketing strategy to attract riders who appreciated that styling. It featured a five-speed gearbox and, on earlier standard models, long, chromed exhaust pipes. The seating typically consisted of a long bench seat, and the overall styling echoed the general design language of Kawasaki's lineup from that period, with ample chrome trim, spoked wheels, and disc brakes front and rear. The claimed wet weight was around 505 pounds.
The KZ750 twin was a somewhat unusual machine, blending retro styling with modern engineering elements, yet not fully committing to either a classic retro look or a cutting-edge performance machine. It was a hybrid that, while respectable, didn't capture the public's imagination in the same way as some of Kawasaki's other offerings.
In the US market, the KZ750 twin was sold from 1976 through 1983, a respectable seven-year production run that indicated a degree of market acceptance, even if it wasn't a runaway success. This production period coincided with the end of the Yamaha XS650's run, further reinforcing the idea that Kawasaki might have been targeting the same customer base.
Legacy and Resale Value
Today, the KZ750 twin models are increasingly rare survivors, often falling prey to customizers looking for affordable, full-size Japanese motorcycles. Their relative unpopularity during their production run meant they never developed a strong cult following, but this has also made them accessible on the used market for enthusiasts seeking a project or a classic ride. Examples can be found modified into scramblers or other custom styles, reflecting the ongoing appeal of these machines to a niche audience.
Key Differences at a Glance
| Feature | 1981 Kawasaki KZ750-E (Inline-Four) | Kawasaki KZ750 Twin (Parallel-Twin) |
|---|---|---|
| Engine Configuration | Inline-Four | Parallel-Twin |
| Displacement | 738cc | 749cc |
| Valves per Cylinder | 2 | 2 |
| Horsepower (approx.) | 60+ bhp | 55 bhp |
| Cylinder Head | Two-valve, SOHC (shim under bucket) | DOHC (shim over bucket) |
| Vibration Control | Inherently smoother inline configuration | Counterbalancers |
| Performance Perception | Sportier, more powerful | More relaxed, less performance-oriented |
| Styling | Typical Japanese sportbike of the era | Often more retro-influenced |
| Production Years (US) | Circa 1980-1982 (as E model) | 1976-1983 |
Frequently Asked Questions
Did Kawasaki redesign the KZ750?
Kawasaki did not fundamentally redesign the KZ750 in the sense of a complete overhaul of its core architecture. However, they did offer two distinct engine configurations under the KZ750 banner: an inline-four (KZ750-E) which was an evolution of the KZ650, and a parallel twin (various models like KZ750-B, CSR). The inline-four saw updates and improvements over its lifespan, but it remained based on the original KZ650 design. The parallel twin was a separate engine design introduced earlier.
How many valves does a KZ750 have?
The 1981 Kawasaki KZ750-E (inline-four) has two valves per cylinder, for a total of eight valves. The parallel twin KZ750 also features two valves per cylinder, for a total of four valves.
How many Kawasaki KZ750 have been sold?
Specific sales figures for the entire KZ750 range are not readily available in the provided text. However, the text does mention that for the parallel twin KZ750, it was Kawasaki's fourth largest seller in spite of its relatively recent introduction in 1976, and that every KZ750 made has been sold. This indicates strong initial demand for the parallel twin model.
Was the KZ750 twin a successful model?
The KZ750 twin had a respectable seven-year production run in the US, suggesting a degree of market acceptance. However, it is described as having "the public never really took to the bike" and that it was not considered a performance leader compared to its four-cylinder counterparts or other bikes in its class. Its success might be better measured by its longevity and its appeal to a specific segment of the market looking for a reliable, traditionally styled twin.
What were the main differences between the KZ750-E and the KZ750 twin?
The primary differences lay in their engine configurations. The KZ750-E was an inline-four, an evolution of the KZ650, offering more power and a smoother inline configuration. The KZ750 twin was a parallel-twin engine, often featuring a DOHC setup but generally producing less power and exhibiting more vibration at higher RPMs, though it was positioned as a more traditional and sometimes retro-styled option.
Conclusion
The Kawasaki KZ750 story is one of adaptation and choice. Whether opting for the refined power delivery of the inline-four KZ750-E or the more traditional character of the parallel twin KZ750, riders were offered a taste of Kawasaki's engineering prowess in the popular 750cc class. While the inline-four model represented a direct enhancement of a successful formula, the parallel twin showcased Kawasaki's willingness to explore different engine architectures to meet market demands and capture specific rider preferences. Both machines, in their own way, contributed to the rich tapestry of Japanese motorcycles from the late 1970s and early 1980s, leaving a legacy that continues to be appreciated by enthusiasts today.
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