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Four-play: 1977-1979 Suzuki GS750

 

Power 60hp @ 8,500rpm (rear wheel)

Top speed 112mph (period test)

Engine 748cc, (65mm x 56.4mm) air-cooled, DOHC, 8-valve inline 4-cylinder

Transmission 5-speed

Weight 511lb (half tank)

Price then/now $2,195 (1977)/$2,000-$4,500          

When Suzuki launched its first 4-cylinder, 4-stroke motorcycle, the company knew it had to build a winner. There was no going back: the days of 2-stroke motorcycles on U.S. roads were coming to an end, and the new bike was running dangerously late against the competition. Honda’s 750 Four, which created the inline quad category, was already seven years old: the hot-rod Kawasaki Z1 had been on the market three years; Yamaha had its DOHC 750 triple — and the mighty XS1100 was waiting in the wings.

Spotting a gap in the market, Suzuki created a machine that was more technically advanced than the class-defining CB750 (by featuring double overhead camshafts) in a more popular capacity class than the Z1/KZ (750cc vs 900cc), and sportier than the shaft-drive Yamaha.

As early as 1974, selected U.S. Suzuki dealers had been able to see and ride a prototype DOHC 750, with their feedback incorporated into the production bike. So when the first GS750s arrived in the U.S. in late 1976, the formula had been enhanced and refined.

Like Kawasaki, Suzuki combined its 2-stroke expertise with current 4-stroke thinking. They designed a short-stroke, DOHC, 8-valve engine with a ball-and-roller bearing bottom end and built-up crankshaft. The short stroke allowed a bigger bore and larger valves for more revs and more power. The bottom end followed 2-stroke practice and proved so strong that drag race engine builders are still using GS-based crankshafts 40 years on!

From the center of the crankshaft, a roller chain with automatic tensioner turned dual overhead camshafts, which ran without bushings directly in the “hemi” cylinder head. Cams operated the eight valves directly with shim-and-bucket adjustment. Suzuki even chose the exact same valve sizes and camshaft timing as the Kawasaki Z1/KZ.

A straight-cut gear on the crankshaft drove the clutch, which was removable without splitting the engine cases, to the 5-speed gearbox. At the rear of the frame, the swingarm pivoted on needle roller bearings (not the rubber bushings used in most bikes) making for more rigid alignment. The 1977 launch bike featured spoke wheels and a single brake disc front and rear — though within two years the updated GS750EC featured cast wheels and dual discs up front.

While being relatively docile and tractable on city streets, the GS really came alive once the tachometer hit 6,500rpm. From there, power came in much more strongly to its peak at 8,500rpm and all the way to the 9,500rpm redline, where it was still making almost 58 horsepower. At the strip, this translated into a 12.75-second standing quarter at 104mph.

And while straight-line performance was a given in the new superbike era, capable handling was not, as Cycle Guide noted of the KZ1000 in its comparo with the GS750. The former would “wallow when we hit any kind of bump when leaned over.” In contrast, their testers praised the Suzuki’s fine handling and relative lack of steering vagueness, something they put down to a rigid frame, combined with the needle-roller-bearing swingarm, relaxed steering geometry and a long 59-inch wheelbase. Steering was also noticeably lighter than the big Kawi with less weight over the front wheel.

Cycle Guide’s criticism of the new GS was limited to a slightly-too-firm seat, over-sensitive rear brake, and some slight oil weeping from the front fork. They summed up: “The GS750 is without doubt the best-handling big-bore Japanese streetbike around … it goes faster and handles better than other 750 multis without losing ground in other areas.” Wrote Cycle in January 1977, “It is without question the best motorcycle in the 750 class,” then nominated the GS750 one of its best five bikes of that year.

Honda and Kawasaki soon released DOHC 750-fours of their own; but the GS750 had sparked a technology race, which led to 4-valve cylinder heads, liquid cooling and aerodynamic bodywork, and eventually gave us today’s race-replica sport bikes. MC

Contenders

1975-1979 Honda SOHC 750F/750F2

 

  • 54hp @ 8,250rpm/ 114mph, 60hp @ 8,500rpm /111mph
  • 736cc (61mm x 63mm) air-cooled SOHC eight-valve inline 4-cylinder
  • 5-speed, chain final drive
  • 525/542lb curb (half tank)
  • Price then/now: $2,148 (1977)/$2,000-$7,000

Honda’s 750 Four K0 of 1969 defined the air-cooled inline four motorcycle for a decade. But by 1975, the DOHC Kawasaki Z1 featured newer technology. Honda’s response was the updated 750F Super Sports, identified by a new 4-into-1 exhaust. At the rear wheel, a disc replaced the mediocre drum. Reduced trail and a longer swingarm preserved straight-line stability, while a stiffer frame and suspension changes improved handling. The engine was claimed to be unchanged, though Cycle magazine recorded 58 horsepower at the back wheel (49 for the 750K), which gave a standing quarter in the high 12s. On the road, the drivetrain and handling improvements together with longer suspension travel made for a comfortable ride and precise steering. The downside: a weight increase of 12 pounds.

New for 1977, the 750 F2 (shown) featured Honda’s problematic ComStar wheels, with triple disc brakes and a new quieter muffler. The engine featured larger valves and more radical cams giving 60 rear wheel horsepower, but at higher rpm.

While they were attempting to verify Honda’s claim of sub-13-second standing quarters. CycleGuide’s test bike dropped a valve, destroying a piston and the cylinder head. The cause, they suspected, was insufficient heat treatment of the valve.

“We didn’t abuse the CB750,” explained Cycle Guide’s review, “but we pushed it to its limits — and then just past.”

That aside, testers considered the F2 to be the best Honda 750 so far, the result of continual refinement and improvement. Honda had created a comfortable and fine handling motorcycle with performance that just about kept pace with the GS750.

1979 Kawasaki KZ750

  • 55hp @ 9,500rpm (rear wheel)/120mph
  • 738ccc (66mm x 54mm) air-cooled, DOHC, eight-valve inline 4-cylinder
  • 5-speed transmission
  • Dual disc brake front, disc rear
  • 491lb curb weight (half tank)
  • Price then/now: $2,749 (1979)/$1,500-$3,000

While it was the Suzuki GS750 that pioneered double overhead cams in the 750cc class, in 1979, Kawasaki struck back with the KZ750. Essentially a stretched KZ650, the Kawi 750’s main advantage was its light weight. At 491 pounds at the curb, it was 51 pounds lighter than the CB750F2 and 20 pounds under Suzuki’s GS750. Though recording just 55 rear-wheel horsepower on the dyno, the KZ stayed with the CB and GS on the strip, recording 12.5 seconds at 107mph for the standing quarter. And while conceding outright performance to both the Suzuki and the then new 16-valve Honda CB750F, the KZ750’s light weight also gave it the edge on the track and in throttle roll-ons — as long as it had 4,500rpm on board.

The secret of the KZ’s sparkling performance lay in its cylinder head, which was designed to breathe freely through ports smoothed with epoxy. This allowed the use of huge 34mm Keihin CV carbs. Below was a plain bearing crankshaft with five mains, Hy-Vo chain drive to the two camshafts and a central gear primary driving the transmission. The engine went into the same KZ650 frame, but with 20mm lower top rails to reduce seat height. Final drive to the cast alloy wheels was by chain, and triple disc brakes provided stopping power.

Testers appreciated the lighter weight of the Kawasaki, noting that motorcycles in general were getting too fat. The Kawasaki proved to be lithe and nimble with good handling, adequate braking and decent comfort. While having no standout positive attributes, “It’s a motorcycle totally without serious fault,” said Cycle World.

Published on Oct 14, 2020
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