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Honda CB 750F1 Supersport
The CB750 transformed the face of motorcycling in three ways. First it set down the design template for the modern superbike with its inline four, high-tech, specification. Second, it cemented the burgeoning Japenese manufacturers as the new force in motorcycling, and, third, its combination of quality, value and performance effectively sounded the final death knell for the ailing British motorcycle industry.
It was the engine that created the most impact: an inline four using lessons learnt from Honda's multi-cylinder racers of the 1960s (but with a single camshaft and two valve heads rather than the racers' dohc and four valves).
Along with enviable smoothness and reliability, the claimed output of 67bhp was mighty impressive for the time - a good 15% more than BSA's then-new 750cc Rocket 3 and, at just under 500lbs, weighted about the same. It's not hard to guess which one won over the buyers.
But it wasn't just Honda's engine that caused a stir. It was also the fact that it was offered in conjunction with a five-speed gearbox, electric starter and front disc brake (the first on a road bike) - and all presented to the consumer at a reasonable price.
Handling, of course, was only adequate, with a flex-prone steel frame and harsh suspension drawing criticism. But that was to be expected and few riders were put off, especially after veteran Dick Mann proved the CB's sporting potential by winning Daytona in 1970.
What's more, its impact was such that Kawasaki delayed and re-engineered its own revolutionary 750cc four-cylinder bike, eventually releasing the Z1m which upped the capacity ante to 903cc, in 1973, and you don't get much finer compliment that that.
A funny thing happened to Honda's new CB-750F Super Sport on its way to market: the bike became what it was only supposed to pretend to be. The intention apparently was to simply generate a more exciting image for the big Four, to create an illusion appealing to the riding sport rather than the sporting rider. They would take a full table-stakes gamble with the CB-400F, giving it low flat bars and rearset footpegs along with a trick exhaust system and breadloaf tank, because the model from which it was derived (the CB-350 Four) hadn't been a winner anyway. But the 750 was, saleswise and otherwise, the flagship of Honda's line and it didn't seem smart to change the bike's essential character. The right approach, it said there in the sales manual, would be to go at this thing very cautiously—give the CB-750's looks a touch of cafe-racer pizazz and a nifty new name; don't mess with anything else.
So, in the fullness of time, a prototype "Super Sport" arrived in America for testing and evaluation—and it proved to be a horror. The bike ran splendidly, because it was a tricked-out CB-750, but it didn't handle at all well. Honda's engineers seem (based on our interpretation of some half-veiled remarks) to have tried trading straight-line stability for ride. They steepened the fork angle—bringing it nearer the vertical—in an effort to reduce stiction and encourage the front suspension to make a more compliant response to highway expansion strips.
They also stretched the bike's wheelbase slightly by
lengthening its swing arm, and this may have been done in hope of restoring a
modicum of the stability lost to the steeper fork angle.
You wouldn't notice the steering geometry and wheelbase differences between the standard four-pipe CB-750 and the Super Sport just standing and staring; the styling differences poke you right in the eye. For one thing, there's that fuel tank, which is a little longer and a lot more skinny and should hold less gasoline. Its capacity actually is greater, up from 4.5 to 4.8 gallons, and that's a good thing because the fuel gets used at a fractionally faster rate. The Honda CB-750 K3 we tested late in 1973 averaged 45 mpg, and would—at that rate of consumption—travel 202 miles before running out of everything but fumes. The Super Sport averages about 43 mpg, goes on reserve (1.3 gallons) at around 150 miles and goes bone-dry at 206 miles.
The other styling trick, apart from the faired extension behind the seat, isn't just styling. Honda has taken note of the popularity of accessory four-into-one exhaust systems, and has made its own for the Super Sport. It has four of the typically-Honda double-wall pipes (each being a pipe within a pipe) feeding into a collector, and the collector exiting into a single, large-diameter muffler. The arrangement makes a lot of sense, even if it wasn't invented by Honda.
A four-cylinder engine's exhaust pulses are spaced apart by 180 degrees of crank angle, and individual pulses have time to travel completely through the muffler alone—the previous pulse having departed and the next not yet arrived. So a muffler with the capacity to handle one of the cylinders will as easily handle all four. That's the theory, and the results with the Super Sport are a convincing argument that it works in practice. The bike's exhaust note is so subdued that most of the noise you hear comes from the drive chain.
We haven't dyno-checked a new CB-750 K5 four-piper, so we can only assume that the Super Sport's collector exhaust system plays some role in the engine's remarkably strong performance. Honda's 750 Fours had seemed to have stalled at, or a little below, the 49.6 bhp mark set by the K2 version provided us for our 1972 Superbike test. The Super Sport felt strong, but until the bike was bolted up against Webco's dynamometer there was no way of knowing whether the feeling was produced by horsepower or the change in gearing.
The tooth-smaller transmission sprocket has an
influence in the excellent quarter-mile figures obtained with the Super Sport;
there's a substantial horsepower difference, too. The CB-750F engine pumped out
an even 58 bhp at 8000 rpm and that's pretty good. Still, the most remarkable
aspect of its performance is that it's there over such a broad speed range. The
engine hangs onto its horsepower a thousand revs above peaking speed and it
delivers better than 33 pounds-feet of torque from 3500 to 9000 rpm. If the
exhaust system was completely responsible it would be quite a piece of plumbing;
some of the improvement is inside the engine.
The Honda Four's disc front brake is so powerful that it hardly needs any help at the rear wheel, but there are times when you have to make moderate use of both brakes and that's a good reason for having discs on both wheels. You may not need all the fade-free stopping power disc brakes can provide, but their smoothly-progressive, predictable action is always a blessing. The big Four is twice blessed by the fitting of a disc rear brake: first because discs are inherently better than drums; secondly because the particular drum brake replaced is a conspicuously poor example of the type.
The standard CB-750 rear brake just doesn't work very well. It's powerful, but difficult to control. The Super Sport's all-disc system is a distinct improvement; one you come to appreciate deeply when you dive into a blind turn, discover that it tightens halfway around, and are obliged to slow for the second half. With the disc brakes' controllability working for you it becomes possible to very precisely divide total tire traction between cornering and braking loads, tighten the bike's arc, and emerge with your nerves frayed, not your hide.
As a matter of fact, the Super Sport's rear brake is
better than the one fitted up front. The front disc is gripped by the pivoted,
single-piston caliper used on the garden-variety CB-750, and the caliper isn't
quite rigid enough to resist flexing when you're squeezing the lever really
hard. This flexing becomes a spongy feel at the lever, and while this doesn't
weaken the braking action—which is strong enough to let you lock the front
wheel—it does make control a little less precise. The rear brake caliper is a
dual-piston design, much more massive, much more powerful, and will not flex at
any pressure up to that required to lock the rear wheel.
Those up front are just red-painted lines incised into the friction material; the rear pads—which may be replaced without dismantling the caliper—have red tabs to tell you when they are worn to the point of bringing the steel backing pieces into contact with the disc. The rear brake master cylinder and brake pedal are carried on a sturdy aluminum casting, and the whole assembly is sure to figure prominently in a number of disc rear brake conversions as it would be easy to adapt to almost any bike.
A serious concern for ride quality led Honda to experiment with the steep fork angle mentioned earlier, and although they had to abandon that ploy, the fundamental concern influenced other aspects of the Super Sport's design. There is, for example, the use of rubber grommets in the front fender mounting to relieve the fork sliders of any binding loads from that quarter. No change has been made in fork travel, but we understand that the damping has been altered and the springs seem to be a bit softer than in earlier CB-750s. Rear wheel travel has been increased from 3.3 to 4.0 inches and the springs softened slightly. The rear dampers are quite different from anything previously used on the big Hondas, and have much more rebound control. Maybe we'd better amend that and say the rear dampers have much more rebound control when new, as those on our test bike did begin to go limp when the odometer turned 750 miles.
That may say as much about the manner in which our
test machines are ridden as it does about Honda's dampers; it still says
something unflattering about the latter.
That assurance was at odds with what we felt in the bike's performance, and it proved to be mistaken. An eleventh-hour telex from Japan brought word that Engineering had, in fact, sneaked in a few performance-oriented engine changes, the full extent and nature of which are as yet unknown. We have learned that higher-domed pistons give the Super Sport a compression ratio of 9.2:1 instead of the K5's 9.0:1, and that the valve timing specifications have been altered to suit the collector exhaust system.
The cylin-derhead for the Super Sport engine carries
a different part number, which would indicate change, but no one at American
Honda could tell us what has been done.
The CB-750F Super Sport's acceleration would be even better, relative to the very similar CB-750 K3, which was the last version we tested, but for a curious weight increase. One would think it impossible that the Super Sport, with its four-into-one exhaust system and single muffler, could be as heavy as the four-muffler Honda Four. And it isn't as heavy as the K3 we tested back in 1973; it's actually heavier. Somehow, somewhere, the big Honda has picked up 12 pounds and now weighs 538 pounds—four less than a Z-1— even though the Super Sport's exhaust system has to represent a weight reduction. We can't account for the difference, having failed to discover anything like a switch to a bigger battery (still 12V, 14AH). We suspect that some of the weight may be hidden away in thicker frame-tube walls. It can't all be in the addition of new brackets—which, by the way, include a trio of drilled and threaded lugs on the forward side of the frame's steering head. These would appear to be mounting points for a fairing.
The above raises a couple of interesting points. First, there's the warning sticker on the lid of a little compartment under the seat, which cautions against fitting the Super Sport with any kind of handlebar-mounted windshield or fairing. Second, there's the fact that Honda engineers have gone to some considerable amount of trouble to pull the heavy headlight back closer to the steering axis, a move that forced the relocation of a bundle of connectors from their former home inside the headlight housing to a molded-plastic box on one of the frame down-tubes. These things add up to a sharp awareness at Honda that the steered mass in a motorcycle is very important to handling—a factor that dictated the rearward brake caliper location on the new GL-1000. Apparently, however, Honda considers that the single light-alloy caliper on the Super Sport's front wheel isn't heavy enough to justify moving it behind the fork leg.
However it may have been obtained—by the revised steering geometry, longer wheelbase, stiffer frame or whathave-you—the Honda CB-750F Super Sport does have exceptionally good handling qualities. Indeed, it is in this area that it comes nearest justifying the Super Sport label. The CB-750F, tighter gearing notwithstanding, is going to get shaded in a straight-line contest of speed with, say, a Z-1. But it handles better than any of the other Japanese Superbikes. Despite the longish wheelbase and stability-oriented steering geometry, the Honda CB-750F handles like a bike at least a hundred pounds lighter.
The Super Sport can be flicked through a series of
esses without all the handlebar-bending effort you have to apply with anything
else in its weight/displacement class, going from a left-peg-dragging attitude
to a maximum-effort right so quickly that you have to start checking the
left-to-right flop well before it is completed.
The requirements for wearing flat spots on the Super Sport's exhaust system obviously include an excess of sporting spirit on the part of the rider—the other factor is simply rider weight. One of our dauntless test riders weighs about 165 pounds in full regalia, and had little difficulty with the Super Sport's exhaust system grounding. Another weighs right at 185, suited up, and he quickly scuffed a nice set of flats on the muffler and collector. A third rider, who pushes the scale past the 210-pound mark, complained vigorously about the bike's lack of cornering clearance. All these experiences were gained with the rear suspension's springs cranked up to maximum preload.
The matter of cornering clearance becomes very important with Honda's CB-750F just because the bike handles so well that it can be cornered at extreme angles. One of our testers (the Hundred Kilogram Wonder) says he was able to provoke a mild wobble in the Super Sport by running it full-throttle into a very fast, bumpy turn but the rest of us found the bike to be extremely steady. The Super Sport's handling is so good that it lets you notice a lot of little things usually overlooked in attempts to compensate for really nasty road manners. For example, you can feel a subtle shift in the way the bike steers when you apply power in a turn and driving torque makes it pitch nose-up slightly. And the Super Sport is steady enough to let you feel the tires working—which they do very well. In all, it gives you the rider a nice, steady platform; it lets you concentrate on watching the road and working the controls, without asking that you wrestle the motorcycle into submission—however you must bear in mind that there is considerable slop in the drivetrain, and concentrate on smooth shifts and even throttle metering to prevent jerky power inputs (and outputs) from initiating suspension wobble or breaking rear tire traction. It has enough power to squirt hard from one turn to the next, the kind of brakes that get you slowed when that's what's needed, and the kind of cornering stability that let's you do some of your slowing clear into the middle of a turn if you've had a lapse of judgment. It's fast, it's fun, and it's safe.
We have mixed feelings about the Super Sport in its
secondary role as a tourer, and it probably is a good thing that Honda will
offer a standard, four-pipe CB-750 K5 alternative. The Super Sport
Apart from the wind-blast difficulties, which certainly are not peculiar to the Honda, the Super Sport is a pretty pleasant thing to ride. Like all big Honda Fours, it has a notchy, won't-be-hurried gear shift mechanism, but then there's so much torque, spread over such a wide engine speed range, that you won't have to do much shifting. Honda Four clutches still have fits of grabbiness, accompanied by loud gronking noises, when the transmission oil is cold; they all seem to work well after everything is up to temperature. Never mind: Honda will eventually fix the clutches, just as the 750 Four's carbure-tion has been fixed. All the earlier Fours we've ridden were afflicted with an off-idle flat spot; the Super Sport was as clean as the Pope's Easter vestments. We don't know what carburetor changes have been made. Whatever they are, they work. Maybe, too, Honda will switch from a ribbed front tire to one with some other tread pattern. The present tires are terrific in what they do for braking and cornering but the ribs on the front tire seem to think they've found a friend when they encounter freeway rain-grooves. Those grooves always wander back and forth, and they make the Super Sport's front wheel wander with them. It isn't a danger; just an annoyance. '
Another annoyance is multi-faceted, and this one
concerns the Super Sport's fuel tank. The tank filler is under a hinged lid,
which is locked, and the latch is stiff enough to make you think you're going to
break the key getting it open. Then, once the latch is sprung and the lid is up,
you have to figure out what you're going to do with the cam-lock filler cap
while gasoline is being squirted in, because the cap is held by a chain that's
just long enough to let it slide down the side of the tank and eventually
scratch the paint. Finally, if you fill the tank and then park the bike, engine
heat will warm the gas, which will then expand and force its way up past the
recessed filler opening, into the compartment under the lid, and out a clever
little drain that feeds into a hose that dribbles the fuel down in front of the
rear tire. It's a fine opportunity for some clown to finish his cigarette and
your new Honda CB-750F Super Sport with a careless flick of the fingers.
Source CYCLE 1975