When the original Honda CB750 came out in 1969, it was the original superbike. All the other OEMs realized it was something new, something they had to counter—or go out of business. Kawasaki realized their own plans for an air-cooled inline four-cylinder four-stroke were now less impressive; the engineers went back to the drawing board, and came out with the Z1 900 for 1973.

To fill its lineup while 900 was under development, Kawasaki sold scary-fast two-strokes, machines that pushed the edge of sensibility and safety. The most famous is probably the H2 Mach IV, a three-cylinder 750 that even today holds a reputation for ridiculous power.

The H2 wasn’t the only machine in this series, though. Kawasaki also had two-stroke triples in the 250, 350 and 400 brackets in the early 1970s, along with the machine that started it all: The Mach III H1 500.

Sixty horsepower does not sound like much these days, and in 1969, Kawasaki missed their goal of building the most powerful production bike in the world. Still, it was scary-fast, thanks to high power-to-weight. Photo: Mecum

Triple power

Three-cylinder engines are fairly rare today, outside of Triumph’s lineup. They were even more rare in the late 1960s, when the H1 500 started development. Most “fast” bikes had parallel twin engines. Four-cylinders had their place on the GP grid, but that tech hadn’t trickled down to the street. It was a simple problem; engineers hadn’t quite figured out how to stop fours and triples from overheating, and besides, everyone else made twins, so why not stick with the plan? Easy-peasy.

But Kawasaki wanted the most powerful production bike in the world, so the boys in lab coats got to work on the N100 Plan. There’s an excellent write-up on the process on Wikipedia, but here’s the basic gist: Kawasaki, with help from Osaka University, developed an inline triple, 500 cc capacity, with piston inlet ports.

Then, Kawasaki sent these engines to the US, where test riders gave them vigorous floggings in the desert heat. Under these extreme conditions, Japanese engineers were able to gather information about reliability, and improve the design.

Pretty tidy and compact, compared to an early CB750. Photo: Mecum

This is a really cool part of American motorcycle history, one that’s pretty much forgotten these days, and one we’ll probably never see again. In the ’60s, there was so much money in the US market that the Japanese were keen to build flagship bikes for American riders. To that end, the factories built their bikes with considerable thought to American riders’ wants, and even involved their US corporate staff in the development process. Then, they’d run the prototypes all over the desert, to see how the machines could be improved.

These days, there’s input from the US market, but it doesn’t have the buying power it used to, and therefore it doesn’t have the same influence. And, you can bet that if the Japanese OEMs were test-piloting some super-duper sportbike all around the southwest, we’d see cellphone spy pix before too long.

This machine has seen an extensive restoration, including many parts re-chromed, and others replaced or rebuilt. Photo: Mecum

Back to the H1 500: In 1969, Kawasaki finally brought the bike to market. It wasn’t as all-around excellent as the Honda CB750, but boy, was the H1 500 fast for its era. It was rated for 60 horsepower around 7,500 rpm, and 41 pound-feet of torque at 7,000 rpm. The CB750 peaked at 68 horsepower and 44 pound-feet supposedly … but it was about 100 pounds heavier than the H1 500. The Kawasaki weighed a relatively svelte 384 pounds dry.

That gave the Kawi a killer power-to-weight ratio. Literally. Back in the late ’60s and early ’70s, the H1 500 had a reputation as a wheelie monster, with rocket-like thrust when you hit the powerband at high rpm. Most riders had never experienced anything like this before, and plenty of crashes resulted. Contemporary moto-pundits pondered whether beginners were able to harness the power. One of Kawasaki’s early test riders supposedly went so far as to call it a “Widowmaker,” and that name stuck with the three-cylinder Kawi two-strokes from then on.

It wasn’t just the abrupt, vicious power delivery. Kawasaki’s two-strokes also had crap brakes, horrid suspension and terrible handling. To be fair, none of the fastest Japanese bikes were considered great in these departments until Suzuki’s GS line in the late 1970s. However, with the H-series two-smokers, the awful chassis made a bad problem worse. The guys I knew who used to race these would always say … nasty … things about the chassis in general.

Along with this nice exhaust, the sale includes a second set to be refinished as the buyer sees fit. Photo: Mecum

Fifty years later

It’s 2021 now, and this 1975 H1 500 is coming up for sale at Mecum’s August 12-14 auction in Monteray, California. It’s in gorgeous shape, thanks to an overhaul by Epicycles Restorations.

The ad says the bike’s brakes and mechanical bits function as they should (“Recent mechanical and cosmetic restoration using the utmost NOS and reproduction parts and 250 hours of labor“). LRC Triples repainted the gas tank, sidecovers and tailsection. There’s a repro toolkit, including no-longer-produced NGK B9HS sparkplugs. The gauges rebuilt, with new graphics; the wheels, fender, headlight ears and other shiny bits were all re-chromed. The grab bar, handlebars, taillight assembly, turn signals and mirrors are reproductions.

The engine itself sees special attention, as you’d expect with a two-stroke (these things have no great reputation for longevity). The crank’s been rebuilt, with new bearings rods and seals. There’s Wiseco rings and pistons, with cylinders over-bored 0.060. The engine gets new bearings, an original refurbished rotor/magneto, a CDI box from Lakeland Services, new plug caps and wires, rebuilt carbs, and so on. This bike has been gone over thoroughly.

You can see a complete list of updates and upgrades at the advert here. As to asking price—who knows what the auction will bring?

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