Kawasaki’s Mach IV 750 H2 Triple

How the big two-stroke drove superbike development.

Kevin Cameron has been writing about motorcycles for nearly 50 years, first for Cycle magazine and, since 1992, for Cycle World.Robert Martin

Kawasaki’s 1972 750 H2 was the most bang for the buck—by far! Find a dealer short of cash and a brand-new H2 could be yours for under a grand. With 74 hp it topped the bike that in put Harley’s Sportster on the trailer, the 1969 Kawasaki H1 500 Triple.

When we got the new bikes at our dealership just before Christmas 1971, we marveled at their simplicity. It was, as one of us said at the time, “Just three giant chain saw motors on a single crankshaft.” Take a cylinder head off and look in: You saw a single forward-facing exhaust port, flanked by two pairs of equal-sized transfer ports. Nothing strange or trick.

H2′s intake system was the simplest: piston-port. Mounted low on the back of each cylinder was a carburetor, feeding its cylinder’s individual crankcase through a hole in the cylinder wall that was opened and closed by the lower edge of the piston skirt as it rose and fell. Intake timing was middle-of-the-road, opening at 75 BTDC, closing at 75 ATDC.

There were two exhaust pipes and mufflers on one side, and one on the other—no coy pretense that this was anything but a triple.

Its musical exhaust sound testified to that. Firing intervals on this triple are equal, just as they are on a twin or a single, but strangely the music is unique.

Mechanics setting up and test riding new H2s revealed tremendous smoke. Hand-mixing oil into the gasoline was over with (and the stains on one knee of your pants that went with it). Yet its replacement—a tiny variable-delivery (coupled to the throttle) oil-metering pump, driven from cross-axis gears from the right-hand end of the crank—smoked badly as ever. A hard plastic line went to one of each cylinder’s two main ball bearings. From there, a rubber-edged oil pickup ring on the nearby flywheel collected oil to a central oil hole in each crankpin. From it, a radial drilling led the oil to each big-end bearing.

Kawasaki’s 1960s two-stroke 250 and 350 twins, A1 and A7, had rotary disc intake valves with their carbs sticking out to right and left (under big aluminum covers), so it was impossible to place a generator and ignition points there. That was a separate unit atop the gearbox, gear-driven. That would’ve been nice for the wide triples (21 inches!), but their keynote was simplicity and low production cost. The A-series twins, with the many O-rings and seals associated with rotary valve, sometimes developed small air leaks. Many times I heard an engine started in the shop, and then heard its revs soar to impossible heights. Turning off the ignition did nothing. Tearing the plug wires off did nothing. The only thing that worked was turning off the tank petcock. We didn’t know it, but we were hearing the opening movement of a symphony now known as HCCI—Homogeneous Charge Compression Ignition. No such problem with H1 and H2.

Like the H1 500, H2 drove a five-speed gearbox through primary gears and clutch on the right side. To reduce the tooth-to-tooth loads in the gearbox (which was dimensionally similar to H1) the primary ratio was speeded up.

1972 Kawasaki H2. Kawasaki

In the past, riders yanked upward, upward on the bars of lesser bikes to make them wheelie. Forget that. A casual turn of the H2′s throttle lifted the wheel. No embarrassing yanking, no throwing your back out. Easy wheelies, any time.

Easy wheelies, any time.Cycle World Archives

As if engine torque wasn’t enough (57.1 lb.-ft. at 6,500), the engine was set quite far back in the style of the times, making wheelies even easier. Official belief worldwide (originating with Gilera and MV in the 1950s) was the notion this would “increase grip.” Wheelbase was 55.5 inches.

Mechanics found that new bikes fresh from the crate had their oil pumps set on maximum, but experience revealed that the lowest setting lubed the engine just fine and didn’t excite other motorists as much.

Overwhelmed Chassis?

Very powerful bikes attract romantic names: widow-maker, bike with the hinge in the middle. One former rider recently wrote that H2 could get you to the scene of your accident quicker than any other. The fact is that there was nothing much wrong with H2′s chassis in terms of strength and stiffness.

What caused the name-calling? Chassis, suspension, and tires that were state-of-the-art in the 1960s weren’t up to 74 hp and the sudden torque hit of a big two-stroke.

There was nothing wrong with H2′s steering geometry; it was period correct, even conservative at 28 degrees rake, 4.3 inches trail. For 1974 power was cut to 71 hp at 6,800, then to 70 for 1975 (were those power cuts to make Z1 look even better?), then rake was modernized to 26.5 degrees with 4.09 inches trail.

What was different about riding H2? One owner said it was a great ride up to 6,000 rpm (which was just below the rpm of peak torque). It was powerful but offered no surprises. But more revs turned it into a mad thing.

This is characteristic of two-strokes with any degree of exhaust tuning. When you approach peak torque, torque almost doubles. On a 250 Suzuki X6 or a Yamaha RD350 this was exciting. On a 750, it was mind-altering. Racers on high-power two-strokes learned to “ride them in the linear range,” which meant staying above that sudden torque jump, never letting it upset the bike while feeling for the grip to accelerate off corners. In the case of Yamaha’s TZ750 racebike, torque pretty much doubled at 9,300 rpm.

People still talk as if there’s a magic way to give two-strokes of the 1970s a smooth, four-stroke powerband. Don’t you believe it!

The late Gordon Jennings, in his acclaimed DIY book, Two-Stroke Tuner’s Handbook, says long, gentle pipe tapers give broad, easy-to-use power. Then have a look at the pipes Suzuki put on its 750 triple racer and see long, gentle pipe tapers. But Gary Nixon said of it, “That’d be a pretty good little motor, if it wasn’t so damn hard to ride.” Hard to ride means narrow power plus a strong hit when the pipes chime in.

Compression damping was <i>spiking to infinity</i> at real-world damper-rod velocities.

Bottom line on two-stroke power? H2 was the pure substance—love it or leave it.

1972, the year of H2′s introduction, was the dawn of a new age that would force manufacturers to rethink the inadequate chassis, suspension, and tires of the 1960s. They didn’t cut it at the 1972 Daytona 200, when Suzuki and Kawasaki both entered race versions of their new street 750 triples. No tire survived contact with 100 hp, so the race was won by little Yamaha 350 twins, easily outrunning the four-strokes and having no tire drama.

Now compare 1971 and 1972. In 1971 the brum-bah folks were reassured by the finish order: BSA, Triumph, BSA, Harley, then a Yamaha in its proper place, down in fifth.

Four-stroke hearts were broken in 1972; the first four-stroke was the Norton of Phil Read in fourth. Upfront it was Yamaha, Yamaha, Yamaha—all embarrassingly small 350 twins. Where were the giant two-strokes? Geoff Perry brought his Suzuki in 14th. No Kawasaki H2R in the top 20.

This provoked a decade of revolution in chassis, suspension, and tires. After a second Yamaha 350 benefit in 1973, Dunlop made a giant belted-bias rear tire, and Goodyear for 1974 defined the coming age—with slicks. This let the violent 750s finish races, blowing all else aside. Disc brakes had already arrived in 1969, making drums into elegant doorstops. Engines and riders were moved forward to keep those powerhouses from wheelying everywhere.

Suspension Revolution

Next a big revolution in suspension damping. The damper test machines everyone used drew graceful flattened-oval curves, but motocrossers knew that was a lie. When damper-rod velocities were measured, and souped-up test machines were built to reproduce them, parts flew everywhere. Damping by pushing oil through orifices produces resistance that increases as the square of damper-rod velocity: the “V-squared effect.” The punch line? Compression damping was spiking to infinity at real-world damper-rod velocities. To fix this, variable-orifice-area damping schemes had to be created; no more infinite compression damping.

Infinite compression damping was especially incompatible with big, powerful two-strokes. Change was coming, but it would take time.

Bad Vibes?

H2s vibrated! This was not for lack of “balancing” but was inherent in having three cylinders whose crankpins were spaced at 120-degree intervals. The result was a rocking couple, a motion like that of a double-bladed kayak paddle. It set the bars to thrumming, and the footpegs and other places. Many parts of the human body became numb.

In March 1975 we called the H2 “Evil, Wicked, Mean and Nasty.”Cycle World Archives

Why wasn’t the triple’s vibration canceled by a balance shaft? All manufacturers buy the products of their rivals and test them. Look at the front wheel of a British parallel twin of the 1960s as it idles on its centerstand. It fluttered vigorously, forward and back. Young men told each other the vibration didn’t bother them. And so H2′s vibration was right in line with expectation.

No More Smoke

The big bad news was the US Clean Air Act of 1970, which would cause Kawasaki (and others) to cancel other big two-strokes it had designed and prototyped (among them Kawasaki’s fascinating “trapezoid”). Two-stroke development was “All ahead stop” as engineers were shifted to a new four-stroke 750 four. No, wait! In every factory there are those willing to receive cash for describing what they see. Industrial espionage. Ah, Honda is coming in 1969 with a CB750 and four cylinders? We must make bigger. That would become the Kawasaki 903cc Z1 of 1973—the first literbike. Motorcycling was taking a completely new direction.

Does anyone think the Clean Air Act was nonsense? I stood at the pit wall, Ontario Motor Speedway in California, 1971, looking straight up. I saw long, sinuous streamers of unpleasant-looking green gas.

Let’s imagine a modernized H2 with its engine and rider moved forward just as Rex McCandless did with his 1950 Norton roadrace chassis concept, and as Kel Carruthers and Don Vesco did in 1971 with Yamaha’s 350 twin racers. We summon, also, the aura of Honda engineer Yoichi Oguma, who smoothed out the Kenny Roberts team’s 500 triple racers with a small gear-driven balance shaft. Carb frothing, be gone! And we recover the normal wheelbase with a longer swingarm, this time strongly braced against twist, just as early Superbike builders were doing from 1977 on. Finally, modern dampers front and rear, with variable-area compression valves—no more spiking to infinity at high damper-rod velocities.

Finally, and most important of all, we could use existing two-stroke direct or transfer port fuel-injection systems to greatly reduce the unburned hydrocarbons (UHC) in the exhaust.

It takes time for new solutions to make their way from track to showroom, but the process is powerfully creative. H2 and its roadrace-version H2R were a major element of the driving force behind 1972′s cascade of new design directions.

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