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Zero

   

Honda CB 750FB

 

 

 

 

Make Model

Honda CB 750F

Year

1981

Engine

Air cooled, four stroke, transverse four cylinder, DOHC, 4 valve per cylinder

Capacity

748
Bore x Stroke 62 x 62 mm
Compression Ratio 9.1:1

Induction

4x 30mm keihin carbs.

Ignition  /  Starting

CDI  /  electric

Max Power

72 hp @ 9000 rpm

Max Torque

67 Nm @ 7000 rpm

Transmission  /  Drive

5 Speed  /  chain

Front Suspension

Adjustable telehydraulic fork. 

Rear Suspension

Swinging arm fork with adjustable shocks absorbers.

Front Brakes

2x 276mm discs

Rear Brakes

Single 300mm disc

Front Tyre

3.50 H19

Rear Tyre

4.50 H17
Seat Height 790 mm

Dry-Weight

236 kg

Fuel Capacity 

20 Litres

Consumption  average

37.8 mp/g

Standing ¼ Mile  

12.4 sec / 172 km/h

Top Speed

198.3 km/h

They said it couldn't be done. They said there was absolutely no way in hell that a motorcycle could really handle with an inline four-cylinder engine sitting upright across its midsection. A four is too big, too heavy and too wide, they said. It has to mount too high in the chassis, they said. They would point to a Ducati, with its narrow, low-slung vee-twin engine, and they'd talk about how it was the best-handling roadster in the world and that no transverse four ever would come even close.

But they were wrong. And the 1980 Honda CB750F—powered by one of those dreaded four-cylinder engines—is proof that they were wrong.

You see, "they"—motorcycling's knowledgeable, influential enthusiasts—underestimated the developmental power wielded by the Japanese. They especially fell short of comprehending the almost unlimited resourcefulness of Honda, whose R&D facility alone is many times the size of Ducati's entire factory. Honda has a track record for making the impossible commonplace, a history that includes starting the trend to four-cylinder street-bikes in 1969. And that, too, was after "they" had insisted that production-line fours would never become a reality.

Ten years later, four-cylinder motorcycles have not only become a way of two-wheeled life, they actually handle. And Ducati's high-flying legend began losing altitude the minute Honda released the 1979 CB750F. For not only did the CBX-styled, DOHC 750 accelerate with the fury of a one-liter hyperbike, it wowed everyone with magical cornering qualities never before found on a four-cylinder street bike. In all fairness, it should be noted that Suzuki actually put the first four-cylinder chink in Ducati's handling armor in early 1978 with its remarkable GS1000. But Honda's 16-valve 750 one year later was the clincher, the first clear-cut indication that the Ducati's cornering capabilities were well within reach of a four-cylinder motorcycle.

It's no surprise, then, that Honda refined the 1980 rendition of the 750F to give it even better handling than the '79. So much better, in fact, that the instant our staff started flinging our test bike through some fast corners, they knew what had to be done: a racetrack handling comparison between the new Honda and a Ducati. Legend or no legend, it was hard to imagine how any comparably sized two-wheeler could possibly out-corner the 750F. So we decided to settle the issue once and for all.

Not just any Ducati would do, however; it had to be the best Ducati. It had to be a Desmo Super Sport, the much-fabled half-racer/half-roadster with desmodromic valve gear, the Ducati with handling purportedly so fantastic that

even a novice could ride like Hailwood. At the time of our test, though, an unsold Super Sport didn't exist anywhere within the Ducati pipeline, from distributor to dealer. So we borrowed a 900 Desmo SS from the privately owned exotibike stable of Earl Smith, Secretary-Treasurer of the AFM (American Federation of Motorcyclists) and a competitor in small-bore roadraces.

With 1500 miles already on the clock, the Ducati was broken-in and ready for peg-to-peg combat with the Honda at Willow Springs Raceway. Better yet, Smith had equipped his SS with the factory's production-racing kit consisting of 40mm Dell'Orto pumper carbs (replacing the stock 32mm pumpers), larger intake manifolds and less-restrictive (but louder) mufflers. We hoped this kit would boost the Desmo's horsepower enough so the Ducati could accelerate on par with the Honda. Our mission, of course, was to compare the two bikes only in terms of handling. But doing so meant that the engine performance of both had to be comparable if data such as lap times and entrance-toexit clockings through various corners and chicanes was to be meaningful.

Having to hop up a 900cc semi-racer just so it could run with a 750cc street bike gives you some idea of how fast the CB750F really is, and why it, too, is called "Super Sport." The factory claims that the F pumps out one horsepower per liter (75 bhp measured at the countershaft), and its 12.41-second quarter-mile E.T. and 125-mph top speed reflect those dyno numbers. But this part of the 750F's performance hasn't changed from the '79 model, for aside from a smaller-pitch countershaft sprocket to mate with the new F's No. 530 chain (the '79 used No. 630), you'll find not one whit of difference in the 1980 engine.

Frankly, we couldn't find much need for any engine changes, either on or off the track. The double-cam four-banger zings up to its 9500-rpm redline so willingly that it's hard to believe that only 749cc are providing so much acceleration. And the engine isn't even cast in the oversquare mold that Honda usually prefers. Instead, the bore-to-stroke ratio is perfectly square (62mm by 62mm), which Honda R&D deemed a reasonable compromise between minimum four-cylinder width (the smaller the bore, the narrower the engine can be made) and maximum valve area (the bigger the bore, the more room available for valves).

With four valves per cylinder, though, the Honda offers more valve area—and more horsepower, as well—than its bigger-bore, two-valve-per-cylinder competition. The light-flywheel engine delivers most of its accelerative vengeance above 6000 rpm, propelling the F-model down the road like something carrying at least another quarter-liter of displacement. Below that engine speed things happen a bit more gradually, but the F still is spunkier down low than any 750-class multi other than Yamaha's XS750 triple.

At lesser throttle openings the Honda acts perfectly domesticated, even though a roadrace-bred lion lurks within. The high-powered F is a lineal descendant of Honda's world-championship RCB endurance racers, yet its exhaust burble is barely audible at idle, and it hums through urban traffic snarls as contentedly as many so-called "commuter" bikes. The 30mm venturi diameters of the F's Keihin carbs allow plenty of high-rpm breathing, and their constant-velocity design, combined with a mechanical accelerator pump, provides cleaner, more-instantaneous throttle response than found on any other bike within shouting distance of the 750 class. Only a slight flat spot when cruising at small throttle openings mars the carburetion, and that's present only because the jetting must be EPA-lean.

Once the CB750F gets on a racetrack, small throttle openings and low revs become the furthest things from your mind. The prescribed go-fast formula is to constantly stir the shift lever and keep the tach needle crowding the red zone. The Ducati, on the other hand, pulls so freight-train consistently from just off idle to its 8000-rpm redline that gear-changing often seems senseless. But as we anticipated, both bikes are about equal in engine performance, even though they get the job done in entirely different ways—the Honda with short overall gearing and ultrasonic rpm and the Ducati with tall gearing and locomotive-class torque.

Actually, almost every significant aspect of the Honda reflects a school of engineering thought that's diametrically opposed to the Ducati's. The SS is powered by a narrow, tandem vee-twin, while the Honda's propulsion comes from a wide, transverse vertical four. The Desmo has a rakish 30.5-degree steering head angle and a whopping 6.1 inches of front wheel trail, but the Honda's steering angle is steep-27.5 degrees, with just 4.3 inches of trail. The SS is configured to be an uncompromised, sport-only street racer, while the Honda is deliberately compromised to serve as all-around street transportation—with, of course, a flair for sport.

But the Honda doesn't feel compromised when it's hammering through a fast turn at full combat speed. Instead, it feels like a flat-out, take-no-prisoners racer. Not in an ergonomic sense, naturally, for it lacks the clip-ons, fairing, rearsets and full-tuck riding position of the Ducati. And not acoustically, either, since the F's high-pitched whoosh certainly isn't as stirring as the thunderous, low-frequency drone issued by the Des-mo. But if what a roadracer is supposed to do is: go precisely where you aim it all the time; bank into a turn at the slightest urging on the handlebar; be so perfectly neutral when cornering that it won't change its leaned-over attitude until you change it; have as much or more cornering clearance than most high-performance twins and singles; and allow you to cut faster laps than any under-one-liter street bike you've ever ridden; then the Honda is a racer, pure and simple. Because electric starter, dual-bulb taillight, upright riding position and all, it executes all that roadracy stuff to near-perfection.

Obviously, the Ducati feels like a road-racer because that's pretty much what it is. But none of our testers was ever able to go around Willow quite as fast on the Duck as on the Honda. And it had nothing to do with the engine and everything to do with the chassis, which, supposedly, is the bike's long suit. The Ducati was as stable as a Greyhound bus on most corners, and aside from grounding—of all things—the bottom of the kickstart arm on hard right-handers, it offered excellent ground clearance. But the combination of narrow clip-ons and mile-long front-wheel trail made steering the SS a real wrestling match. Once banked over into any particular corner, the Ducati was wonderfully willing to stay that way, but getting it into or out of that lean-angle called for lots of muscle on the grips. That slow steering tended to make the SS run wide going into some turns, whereas the Honda would obligingly and obediently follow whatever line the rider picked, be it inside or outside.

Worse yet, the Desmo would wobble ferociously at Willow when accelerating hard out of Turn Two's increasing radius, and also while sweeping through fast-and-bumpy Turn Eight. And it could even be made to wiggle nervously on some fast back-road corners. The Honda never wobbled on the road, and the worst thing it did on the track was to just sort of "move around a little," as Gingerelli put it, in Turn Eight.

The Ducati's disco-dance was a byproduct of its low-tech Marzocchi rear shocks, which suffer from an abundance of spring rate and a scarcity of rebound damping—perfect suspension tuning for a pogo stick. The front fork also is firmly sprung but at least it has sufficient damping to preclude any similar problems. The front wheel would, however, chatter heavily in some of Willow's fast, bumpy corners.

Conversely, the Honda's low wigglefactor is largely due to the quality of its suspension. The fork is compliant, yet fully able to keep the front wheel under control both on and off the track. And the '80-model's FVQ shocks offer two externally adjustable settings for their compression damping and three for rebound. Turning a notched ring atop the shock dials in the rebound while a lever protruding from the lower shock-mount clevis selects the compression damping. For racetrack use we settled on the firmest rebound damping and the softest compression setting, with the spring-preload cams on one of the two highest (of five) notches. Turning everything to full soft gave a pleasant street ride with, surprisingly no wobbles until the rider of pretty aggressive in fast turns. The ride still doesn't top that o the Suzuki GS1000, but it's getting close.

Those Showa-built shocks can only take part of the credit for exorcising a slight wiggle that sometimes cropped up in the '79 750F. The 1980 chassis recipe calls for a heavier-walled swingarm, additional frame gusseting and increased wall thicknesses around the swingarm area, plus a larger-diameter pivot axle that floats in needle bearings. These refinements, and the F's new reversed-spoke ComStar wheels, have tacked almost 15pounds onto what was one of the lightest 750 multis of all. Even though the black-painted spokes on the new wheels are aluminum, the complete assemblies weigh more than last year's steel-spoked ComStars. Apparently, the added weight stems from Honda's decision to make the wheels strong enough to be used on heavier models.

Despite its increase in weight, the 524pound 750F still feels like motorcycling's lightest 750 multi any time it's moving. And much of that has to do with "mass centralization" Honda-speak for the company's current philosophy concerning centers of gravity. Since the center of gravity (cg) of a wide-engined four obviously can't be as low as on, say, the narrow-engined Ducati, Honda tries to concentrate as much mass as possible as close as possible to the cg. This reduces the bike's polar moment in all planes, which is like saying that it reduces the flywheel effect of the entire motorcycle as it leans and turns. Heavy parts, such as the battery and the exhaust system, are moved closer to the cg, and things that live at the extremities of the machine and can't be moved—fenders turn signals, seat base and such—are made from the lightest material that's practical, which is plastic on the 750F. The shifts in the location of components are generally subtle and the weight-savings often only a few ounces; but if it's done well, as it seems to have been on the F, a heavy motorcycle with a fairly high cg can feel lighter and be more responsive than a lighter bike with a lower cg that has its mass more Bread-out.

Whatever the reasons, the Honda maneuvers effortlessly, whether wailing into a 100-mph racetrack turn or swinging into the Safeway parking lot. The quickish steering geometry allows the F to react instantly to the rider's commands, as opposed to the Ducati's geometry which seems intended to boost rider confidence by providing an uncommon amount of directional stability. You can take your eyes off the road while riding the Desmo—or even accidentally move the handlebar—and fully expect that the bike won't wander off-course as a result. Not so the ultra-responsive Honda which, like so many classic British motorcycles, demands participation. If you don't remain an active pilot, the thing might divert off-course, and if you unconsciously nudge the handlebar, it will.

Despite their vast differences, though, both motorcycles handle exceptionally well. And in the end, determining which handles best is a matter of tenths. While barreling along a winding road at, say, eight-tenths, the Ducati probably handles better or at least feels like it does, to riders less-experienced in the art of backroad blitzing. The Duck is the Rock of Gibraltar at that pace, so stable and predictable that it lifts that rider's level of confidence about two notches. The Honda is marvelously responsive and always eager to peel off into a fast bend, but these same riders may not care for the ever-present need to stay on top of things—not at eight-tenths, at least.

At nine-tenths the Honda begins gaining the upper hand. The Desmo makes you work harder than the Honda does, and the Duck's rear shocks start letting the rear end get disturbingly rubbery. Nonetheless, at this point, a good rider can go just about as fast on either bike.

But not at ten-tenths. Not when you've thrown caution to the winds, when your adrenaline is pumping furiously and the whole world consists of just you, the bike and the asphalt. That's when the Honda emerges as the clear-cut victor in this two-bike handling showdown. It lets you go faster with less work and more control, even with 115cc less engine displacement. And ten-tenths is where the Ducati lets you know that you've just pressed it past its limits. The rear end wobbles and jounces, the steering resists inputs and the SS is no longer a confidence-inspiring wunderbike. At ten-tenths, The Legend officially changes hands

Source Cycle Guide of 1980  

 

 

 

NOTE: Any correction or more information on these motorcycles will kindly be appreciated, Some country's motorcycle specifications can be different to motorcyclespecs.co.za. Confirm with your motorcycle dealer before ordering any parts or spares. Any objections to articles or photos placed on motorcyclespecs.co.za will be removed upon request.  

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