Green Meanie! Evolution Of A Two-Stroke Beast

Riders must be of a certain age to have fond memories of two-stroke motorcycles, let alone that of the infamous "Green Meanie" variety. Two-strokes (or "two-smokes" as they're affectionately called) burn oil with gasoline, producing prodigious amounts of smoke from their tailpipes. They have a particular exhaust tone, often characterized by "ring-ding" sounds and a recognizable scream when revved.

It's easy to tell them apart from four-strokes by sound alone. Old-time motorcycle racers firmly believed two-stroke exhaust tones were the sound of proper racing machines. Many would back that statement today.

The two-stroke platform is simpler compared to four-stroke. Unlike four-strokes, two-strokes have no valve train and are therefore lighter. Sensitive to exhaust design, piping to eject exhaust gases evolved into bulbous "counter-cones," known today as expansion chambers.

Zephyris, Wikipedia

Riders highly value accurate carburetor tuning with two-strokes, as these engines can seize if jetted too lean. This can cause spectacular crashes should the rear wheel lock up. Wise riders keep two fingers on the clutch lever, hoping to quickly squeeze and prevent catastrophe.

Another characteristic of the two-stroke motor is its power delivery. Its power band builds slowly, then abruptly spikes with a large, narrow "step" in output. Difficult to ride, the power spike can cause large, unexpected wheelies or a high-side crash, which were frequent and sometimes career-ending.

The Early Widowmakers

Before the Green Meanie handle was born, Kawasaki produced two notorious three-cylinder, two-stroke models. The 500cc H1 Mach III arrived in 1968 followed by the 750cc H2 Mach IV in 1971. Both had period-design suspension, frames and brakes ... none of which were effective in controlling the power output from their motors.

Considered unachievable by motorcycle experts of the era, the H1 was able to travel the quarter-mile from a standing start in 13.5 seconds. Their frames would flex under braking, acceleration and cornering loads, which earned them the nickname "flexi-flyer." But by God, they were crazy fast and people loved 'em!

Jump to 2014 and the H2 moniker's insane performance picks back up with Kawasaki's research/development team releasing a supercharged, inline four-cylinder, four-stroke motor.

Kawasaki initially released it in the H2 and H2R sportbike models, equipping the track-only H2R with 330 horsepower. Kawasaki later introduced two more supercharged models with that same motor: the H2 SX, a sport-touring model and the Z H2, a "super-naked." One tester referred to the latter as a "deranged, lunatic of a motorcycle".

But I digress. In 1974, authorities changed homologation rules, reducing the cost to develop and race new-design motorcycles. As a result, Kawasaki decided to build a new two-stroke race machine for the Gran Prix and American racing contests.

Kawasaki's K2R, A Mean Precursor

The K2R air-cooled motor had not been without development problems. In 1973, the American Motorcyclist Association (AMA), as a member of the Fédération Internationale Motocycliste (FIM), agreed to follow FIM rules for a new Formula 750 World Championship series. Prior Kawasaki racing motors used special-cast, race-only cylinders but new FIM rules required stock cylinders, crankcases and heads.

The problem was that Kawasaki designed the outside cylinders on the stock production motors with the exhaust ports angled outward, which would not work with the narrow frames of the race machines. Kawasaki solved this by swapping the outside cylinders so the exhaust ports angled inward but the team removed many cooling fins on the cylinder sides. With limited engine cooling, seizures became a problem, making tuning a critical issue.

During the evolution of the K2R, improvements in aerodynamics and fuel stop adaptations brought notable success, securing their use in future racing endeavors.

B. Cox, Rand Hall

Randy Hall, who combined team management and development engineering roles to lead Kawasaki's racing program from 1973 until the end of the F750 era in 1976, became interested in the aerodynamics of their race machines.

During the late 1960s, Jerry Branch, a friend of his, evaluated a streamlining kit in Caltech's wind tunnel, adding almost 10 mph to Harley-Davidson's V-twins around Daytona's banked oval.

Hall felt the rounded tail section of the KR750 was not aerodynamic enough. He loosely copied Branch's design, bettering airflow over the back of the rider and rear of the motorcycle. He then added a small raised lip at the tail, gaining stability while reducing drag.

A second improvement came out of three-cylinder fuel consumption issues. The slower four-strokes could race all 200 miles of the Daytona 200 without stopping. Three-cylinder Kawasakis were faster but with poor fuel economy, they had to refuel mid-race.

Hall turned to his engineering roots and developed the first fast fueling system for motorcycle racing. It consisted of a 30-gallon fuel can perched on a 10-foot-tall stand. Its large diameter fill hose plugged into quick connect fittings on the motorcycle.

The crew installed fittings on both sides of each fuel tank, as races ran in both counterclockwise and clockwise directions. That system, still in use today, was able to pour five gallons of fuel every five seconds. The team resolved many issues, including venting, overflow and safety concerns, by requiring a "dead man" valve to be held open during refueling (flow stopped if released).

Now all they needed was a top-shelf motorcycle to match their scientific swagger.

Enter The Greeniest, Meaniest "Green Meanie" Of 'Em All

The newly designed racing machine, a replacement for the air-cooled K2R, was known internally as the 602 but the racing world knew it as the KR750. The American Motorcyclist Association approved it for racing in 1975. Capitalizing on the base design of the Mach III and Mach IV motors, it had three cylinders but, unlike the street versions, was liquid-cooled.

Kawasaki engineering simplified the design of their motor, resulting in less weight and better power transfer through the engine internals, especially when compared to Yamaha's overly complex TZ750.

Kawasaki improved the 602 in 1976 by adding upgraded brakes and forks, then relabeled it the 602L. Other improvements included magnesium crankcases and a new clutch, significantly reducing the weight of the machine. The replacement 602L won races and set lap records but even with less weight and more horsepower, it struggled to beat the original 602 with its absolutely savage power delivery.

Kawasaki's factory budget was limited, at one point delivering cylinders to UK teams without cast ports. Team mechanics got the job done using data supplied by Kawasaki. English and Australian teams tested and updated their suspension, brakes and lighter wheels.

Team Kawasaki Australia modified its sole KR750 in 1978 to incorporate Brembo front calipers, Zanzani plasma-coated alloy front discs, specially made Campagnolo wheels and an alloy fuel tank, further reducing weight.

Unlike the Yamaha and Suzuki motors, which engineers tuned for a more linear torque curve, Kawasaki tuned the KR750 "Green Meanie" similarly to motocross engines of the era. Its chassis, proven strong, was still no match for the motor's brutal power-twisting and weaving under acceleration. It's that power that provided speed ... and wins.

Officials timed one of the Green Meanie KR750s at 192 mph in the 1978 TT.

Exit Stage Left (Cult Of The Green Meanie)

Today, two-stroke road bike manufacturing is legally dead. Despite a strong racing following from champions like King Kenny Roberts, who eventually raced a two-stroke engine of his own design, the two-stroke's days were numbered. Emerging concerns about greenhouse gases and exhaust emissions took precedence and after the 2002 season in motorcycle Grand Prix racing, organizers replaced two-stroke motors with four-stroke motors.

But some people just can't leave the past behind. German enthusiast, Ralf Kraemer, owns and loves the old Kawasaki two-stroke triples. He administers their only German-speaking forum, Triple Klinik GL, and owns quite a few.

He owns an original KH500 and has kept it for 30+ years.

He built a tribute KR750 and calls it his "KR800". Starting with a 1972 Kawasaki H1B frame, his machine looks strikingly like the Kawasaki race bikes 602 and 602L. The engine was a Mach IV 750cc, bored out to 800cc.

The builder claims riders can pilot his KR800 like a modern sportbike, with no wobbles and excellent performance. Mr. Kraemer is also on social media. Follow him on Facebook and Instagram.

What's Your Favorite Historic Road Bike?

A lot of great riding history still awaits documentation. Which tales are your favorite and why? Your input is invited. Leave a comment and/or write an article!