Motorcycle Classics

Take Five: 1985-1991 Yamaha FZ750

Yamaha FZ750
Claimed power: 85hp @ 11,000rpm (period test)
Top speed: 140mph (period test)
Engine: 749cc liquid-cooled 20-valve DOHC inline four
Weight: 494lb (wet, no fuel)
Fuel capacity/MPG: 30-50mpg
Price then/now: $4,599 (1985)/$1,500-$4,000

Sales people love something new to talk about. And in 1985, the plaid jacket guy at your Yamaha dealer could claim one-up on the competition. Their bikes only had four valves per cylinder. His new FZ750 had five. More is better, right?

Well, maybe. The move to 3- and 4-valve cylinder heads was spurred by a need for more efficient combustion (read: lower emissions) while using higher compression ratios (for higher performance) but running with the new, lower-octane unleaded fuels. More valves also meant a lighter valve train allowing higher revs while maintaining good gas velocity at low revs for tractability. But five? As the only manufacturer going for the handful, Yamaha had something to prove.

And prove it they did. In the new FZ750, the 20-valve Genesis engine churned out 85.3 horsepower at a screaming 11,500rpm on Cycle magazine’s dyno. It also tore up the quarter-mile strip in 11.4 seconds at 117mph, and hit 60mph in less than three seconds. “It’s hard to conceive of this level of power from an over-the-counter 750 engine,” Cycle’s editors said, adding, “yet the FZ delivers the goods so eagerly it makes other 750s seem as if they belong in a race for freight elevators.” And it wasn’t all top end power. “The engine is remarkably tractable, too, considering its high specific output, and that’s largely due to the copious midrange. Usable power comes on at 3,000rpm and builds smoothly to the 11,000rpm redline,” Cycle Guide said.

All this grunt came from an inline 4-cylinder with chain-driven dual overhead camshafts, 11.2:1 compression and the aforementioned 20 valves. Each cylinder had three 21mm intakes and two 23mm exhausts arranged radially in a shallow “biconvex” combustion chamber and adjusted by under-bucket shims. The 68mm pistons ran in “semi-wet” iron liners (with coolant contacting the liners only near mid-cylinder), connected to a crankshaft with a 51.6mm stroke. Drive to the 6-speed transmission was by straight-cut gears and a wet multiplate clutch. The 300-watt alternator was piggy-backed on the crankcase to minimize engine width.

The drivetrain was slotted into a square-section steel tube perimeter frame with the cylinders canted forward at 45 degrees, allowing the four 34mm downdraft Mikuni CV carbs to breathe cool air from above the engine in front of the gas tank, while also providing an almost straight intake tract. The forward slant also gave the FZ a lower center of gravity, and, Yamaha hoped, would help mitigate the familiar inline 4-cylinder engine buzz by changing the plane of primary vibration.

An air-adjustable Kayaba front fork (absent the then-popular anti-dive fitments) with 39mm fork tubes controlled the 120/80 x 16-inch front tire by a steep 25.5-degree rake, while a single, multi-adjustable spring/damper unit and swingarm held the 130/80 x 18-inch rear. Triple discs — two up front and one out back — provided braking.

How did all this work in practice? Cycle Guide’s tester found that, in spite of the steep steering angle and 16-inch front wheel, the FZ750 was slower to turn than some other sport bikes at moderate speeds, but that it had “… rock-solid stability. Pump up the pace closer to racing speeds … and the steering lightens considerably,” they said, “permitting reasonably quick transitions, and the bike adheres tenaciously … as if Eddie Lawson programmed each FZ at the factory.” Cycle Guide put much of this down to the “stout” steel frame.

However, testers also found the FZ’s handling to be sensitive to front fork air pressure and rear preload/damping settings, not to mention tire pressure. “You can work around the rear suspension at almost any setting; it’s very forgiving,” one Cycle tester said, adding, “But front tire pressure is so critical that a change of 2psi makes the difference between a solid stick and cut-and-thrusting yourself up a cactus when the front end starts to push.” As for comfort, the combination of a “racer-crouch” riding position and engine vibration in the 4,000 to 5,000rpm range also meant “every tingle and expansion joint makes itself obvious,” testers said.

None of that kept the motoring press from ultimately praising Yamaha’s 5-valvers. “The FZ is breakthrough technology of the most exciting kind, exacting yet usable, specialized without becoming single purpose,” Cycle said. “It offers class-leading horsepower and possesses superb handling as well as composure and feel that’s clearly the result of race-track knowledge,” Cycle Guide concluded. “It’s the blueprint for sport bikes of the future. Or at least for those that expect to compete with the FZ750.”

Contenders: Sporting rivals to Yamaha’s FZ750

1985-1987 Suzuki GSX-R750
Claimed power:
79hp @ 11,000rpm/142mph
749cc air/oil-cooled DOHC inline four
437lb (wet, no fuel)/30-47mpg
Price then/now:
$4,299 (1986)/$1,700-$4,000

The GSX-R750 marked a turning point in Japanese motorcycle design: until then, more power came with more weight. The Gixxer simply nixed the weight. Suzuki claimed 388 pounds “dry,” though testers found the bike weighed in at 437 pounds ready to ride but without gas. Still, it was significantly lighter than the FZ750 and the Honda VFR750F. How’d they do that? By combining an air/oil-cooled engine with a light aluminum frame — and by starting the now-familiar process of paring away weight from every single component.

Lighter though it was, the Suzuki was down on power compared to its competition — 79.26 horsepower according to Cycle’s dyno; air/oil engines require looser tolerances than liquid-cooled engines. But its light weight gave it comparable performance on the drag strip, with the Gixxer posting 1/4-mile times within hundredths of a second of the FZ at a similar terminal speed. And in the twisties, with its 18-inch front wheel and then-new radial tires, the Suzuki offered lighter handling, feeling “planted yet flickable,” Cycle magazine said.

However, Cycle also spotted another familiar sportbike trend: uncompromising ergonomics. “The seating position that lets the Suzuki work so well at the racetrack and in the canyons cannot translate comfortably to highway use. Arms tire quickly, legs cramp up,” they said. Overall though, Cycle noted, the trend was clear: “The Suzuki convinces us that the future is low mass.”

1986-1989 Honda VFR750F Interceptor
Claimed power:
82.5hp @ 10,500rpm/144mph
748cc liquid-cooled DOHC 90-degree V4
476lb (wet, no fuel)/33-55mpg
Price then/now:
$5,298 (1986)/$1,200-$4,000

On paper, Honda’s new-for-1986 VFR750F looked a lot like the original 1983 VF750F V45 Interceptor. But damage control from catastrophic valve train issues in the older chain-driven overhead cam version required Honda to change just about everything on the engine except the bore and stroke. The new engine was physically smaller, lighter, more powerful (thanks to better breathing) and more reliable because of improved oiling, gear-driven camshafts, and revised valve operation with each valve driven by its own cam lobe and rocker versus the paired setup on the earlier engine.

The revised 16-valve engine, now with six gears (up from five), went into an aluminum perimeter beam frame (instead of steel as in 1983) as a stressed member. The chassis was fitted with an anti-dive fork with 110/90 x 16-inch front tire and adjustable single-shock swingarm with 130/80 x 18-inch rear.

The new VFR became the pacesetter in its class — which included Yamaha’s FZ750, Suzuki’s GSX-R750 and the new Kawasaki 750R Ninja — recording a sub-11 second quarter mile at 120mph and being fastest around the Willow Springs circuit. It also vied with the Ninja for favorite street bike.

The new Honda was “the best sporting 750 in the world,” Cycle Guide wrote. “The V4 engine is faultless.” More significantly, the basic Interceptor plot has endured with little change right to the present. MC

  • Published on Aug 15, 2014
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