A Review of the CBX750 From the English 'Superbike' Magazine

Last year the CBX was the fastest 750 ever. But then a year in motorcycling is an awful long time.

Memorable rides maketh the motorcycle and I have plenty of good memories of Honda’s CBX750. In two weeks and 1400 miles it got a real hammering around test tracks, along countless motorways and especially along the wonderfully fast and flat A-roads of France. It emerged as a very impressive, professional motorcycle with few limitations. At home and abroad, in fair weather and foul, its ability (as well as its dual 60W headlights) came shining through.

It’s fairly fast and fairly flash. Paradoxically, it’s also fairly faceless. Its only outstanding character is of all-round competence. The engine is the most powerful Honda 750 unit ever. Handling and steering are excellent. Braking and roadholding are good but could be improved by better rubber. The Super Sports tag is spot-on. Touring is very much a question of how fast you need to go for how long. It’ll cruise all day at the ton; much above that though and you’ll need to rest your neck muscles every third day.

Launched last year and deliberately upsetting the balance of Honda’s V4 big bike range, the CBX was rightly acclaimed and admired by the press, though I’ve hardly ever seen any on the road. I saw two at Le Mans and one of those was being raced. It was expensive last year but at £2859 is less so compared to this year’s hot-shot 750 competition. There again, the opposition has moved on. Suzuki’s GSXR, Yamaha’s FZ and Kawasaki’s 750R are all bristling with new technology and sheer speed. Suddenly last year’s fastest 750 finds itself in fourth place. So it goes.

Realistically, em-pee-aitch figures above 125mph count for little even to serious road users. On the autoroute back from Le Mans, I was holding a constant 110mph with the occasional blast up to 120/125mph. A lot of Ninjas, FJs even RTs came past but I’d soon peg them back and leave them behind. Speeding in someone else’s country is always fun if only because you take liberties you wouldn’t take at home. Anyway, the point is the CBX was going faster for longer than any of these bigger bikes wanted to go.

The most I ever saw out of this model was a disappointing 130mph. It wouldn’t redline in top, turning just over 9000rpm in sixth, some 500 revs short of maximum poke. The engine was 500 miles young but not noticeably tight. It was going rather better at the end of the test period some 1400 miles later and revved out perfectly on the dyno. On the road through France I’d probably upset the streamlining a bit by lashing panniers and a tote bag on the back. Whatever, it never made more than 130mph against the wind, whereas we saw 135mph out of last year’s test bike and even 137mph in a back-to-back sprint with a VF750. The CBX is definitely the quicker of the two – 91hp against 90 and an extra mph or two against the stop.

It sure is compact. Honda have pruned engine width, height and length in a number of clever ways. Width is saved by the common expedient of mounting the alternator behind the cylinders. It’s chain driven from the crank centre and has a high 320W output to cope with the juicy demands of the twin headlights. The roller bearing, brushless generator spins at over twice the engine speed, sports an integral fan and a housing with cooling air ducts plainly visible on the left side of the engine. It also features a driveline shock absorber. Even so there is some occasional driveline vibration above 100mph. Impossible to pinpoint; all you know is that there’s something running sporadically harsh in the transmission department.

Primary drive is by direct gear from the crank, no jackshaft in sight. Instead one web of the crank has been made into a gear pinion (it’s just inside number four cylinder) which drives the clutch direct. This keeps the motor short. Engine height has been reduced by using a smaller oil sump and redeploying the frame downtubes to double as oil carriers. Total capacity is actually increased. Moreover, the trimmed motor can now be mounted lower in the frame for better handling.

It feels low and compact too. With a wheelbase of 57.7in, a seat height of 31.3in and a generous 5.7in of ground clearance, the CBX has absolutely nothing in common with the rest of Honda’s 15-year range of countless, inline four, CB750 incarnations, ie it handles a treat. I tried hard to deck something on this bike and failed miserably. Maybe I just didn’t need to, it seemed to get through all the corners plenty fast anyway.

The steering is nicely quick. The fairly wide bars are angled slightly towards you and offer perfect control over the naturally quick-steering 16in front wheel. The aluminium fork brace looks a bit minimalist but the 39mm air-assisted teles give a firm, trustworthy front-end ride. I ran 10psi in them (Honda recommend 0 to 6psi) and left the rebound damping and one-sided TRAC anti-dive on the recommended mid-way settings. At the back and with some difficulty, I squeezed 50psi into the Pro-Link (the manual says 0 to 57psi). The result was a nimble and extremely well-damped ride. It was perfectly stable in a straight line except for the one bowel-moving occasion when a demon gust of wind (I think) lifted the front wheel into a 120mph airborne skip. The rest of the time it was easy-peasy going flat and holding wildly onto the bars.

The fairing may be aerodynamic but the windblast still hits you square in the face. Built in three main sections plus screen (and consequently cheaper to replaced if damaged) the 120mph ride became a strain on the neck after a long session in the saddle. After four hours at 100mph-plus, I was forced to slow down simply because the muscles could no longer support my head and helmet. The sports fairing, although fairly efficient at deflecting the windrush away from your body, tends to rattle a bit at speed. You notice things like that because the CBX is uncannily quiet on the move. There’s hardly any engine noise thanks to the much-praised and described, maintenance-free hydraulic tappets. Sure there’s some driveline vibration that tends to come and go, especially at the top end, but through most of its power range the CBX is smooth, civilised and strangely quiet.

My brief rides on it last year had convinced me it was a narrow-powerband engine with all the real poke living 8000rpm and upwards, necessitating constant stirring of the six-speed box. Two weeks with it have taught me different. It actually pulls strongly and cleanly from below 4000rpm with a big increase between 6000 and 7000rpm, above which it just piles on the horses in big gobs of power right up to 9500. On the road, 7000rpm equals 100mph and it’s perfectly tractable throughout its range. On the dyno it made 84.4hp at the rear wheel at 9500rpm. Honda claim a maximum of 91 at 9500 so, for once, the manufacturer’s quoted output is not wishful thinking.

Around the test track where input is obviously more severe, its peakiness became more apparent. It lacked a bit of snap out of the corners unless the motor was spinning 7500rpm or more. Even so it was making enough horsepower to slide the rear tyre. The Jap Dunlops (130/80 rear and 110/90 front, running 42/36psi) aren’t bad tyres though you could definitely improve upon them. The rear was well-wrinkled by the end of the test.

The brakes are good but the front has a lot of lever travel coming almost back to the bar even when perfectly set up with new pads. Some fade was noticeable after repeated heavy use at the track. The rear is very powerful but proved useful on the road. I can’t say I noticed the one-sided TRAC anti-dive.

The hydraulic clutch is pudding-like, no feel at all and no different in launching from a line whether it’s fed in against a torrent of revs or just dumped. It’s got a weird, heavy-ish pull. Better to ignore it altogether since the gearbox is super-slick with a light action. The six ratios are close and well chosen but for sixth, which is a tad too high in the teeth of a moderate wind.

I really didn’t care for the two dummy plastic bellmouths (fitted to number one and four carbs only and carefully dinked in at the top as they come off the production line so the tank will fit) nor for the seat which is too narrow and has a rock-hard lip that makes sitting well-forward a bit uncomfy. The mirrors, controls, pegs and instruments are mostly excellent, push-button indicators and main beam switches with nicely laid out, easy-to-read clocks. The fuel gauge was overtly pessimistic, indicating that the 22lit/4.8gal tank was dry after only 125 miles or so. In fact, the best full tank range recorded was only 147 miles (the switch was on reserve and the rider was distinctly edgy). Normally it was filled up before the 130 mark. The best return was 40.8mpg, the worst 30.2mpg (we saw it down to 26mpg last year) and the 1000-mile average was 36.5mpg. It’s thirsty but then it does offer a lot of performance. Use the plentiful acceleration and you have to pay for it at the pumps.

At 4901b dry, you wouldn’t expect the CBX to be a sharp-handling scoot but it really is flickable for a 750, moreover it never feels heavy on the move or at a standstill. It feels low and light thanks to an impressive combination of a quick-steering front end which is low in frontal area plus excellent overall weight distribution (48.6/51.4 front and rear) which is very close to the 1.1 ideal.

The frame is completely tubular but has been computer designed and has some notable features. For a start it’s got an extremely heavy-duty, large-diameter rear loop. The front downtubes double as oil reservoirs. Overall the double cradle is smaller, it’s been longitudinally shortened and vertically lengthened to give both a compact wheelbase and easy access to cylinder heads and even the block (no more removable side rails).

The 120W main beam, twin-headlight output is remarkable for a production bike. Anybody who caught the late Sunday Calais ferry after Le Mans will appreciate the point. It was dry for the entire crossing until you got within 400 yards of the grey cliffs of Dover where it was hammering down. Rain and fog all the way back to London, but at least I could see what I was running into (ie, yet more rain and fog).

A few other details command attention. The Honda air gauge in the toolkit was the only one among my huge personal collection of such gauges that actually gave a reading off the Pro-Link. The side panels and ducktail got scratched from the bungeed-on panniers and bags. If the rev limiter that cuts in at 10,800rpm was working, I certainly didn’t notice it. Finally the colour combinations, red and black or all silver, are visually stunning. The CBX is a very sleek and sharp-Iooking sportster.

There’s very little to choose between the CBX and the VF based on performance alone. The CBX is a shade quicker and a lot peakier. The VF is a pure sportster that needs a lot of setting up. Also it’s inherently complex and has been plagued with problems (see this month’s SuperSurvey). Against that the CBX is notably maintenance free (no pitted cams reported so far, plus it has a cam chain tensioner that pulls rather than pushes). Also the CBX is really easy and safe to go fast on. It’s marked by exceptionally easy steering, fast handling and sheer grunt. The V4 is a technically more interesting and probably superior motorcycle. But at the end of the day the CBX is easily the best inline 750 Honda have ever made. For those not seduced by the V4’s new-wave appeal, that fact alone might prove enough.

Conclusion

Subjectively as well as objectively, the Kawasaki is better than the Honda in almost every respect. Through a series of corners, the Honda has a tendency to push straight on where the Kawasaki just tracks accurately along the chosen route. The Honda’s steering is perhaps slightly quicker than the Kawa’s, especially at lower speeds, but the Kawa has a feeling of solidity on the road that isn’t quite there on the CBX. The Honda’s fairing is less than perfect at high speeds, simply because of its relative smallness, but the Honda is easier to ride at night thanks to its powerful twin headlight setup. Both brakes and hydraulic clutch felt spongy on the CBX, as did the Kawasaki’s clutch (also hydraulic), while the GPz’s brakes are very probably the best currently available on a production machine. Comfort-wise, the Honda scores with nicely compliant suspension arrangements and a lightweight gearchange, and the engine is certainly mechanically quieter than the Kawasaki’s collection of churning gears, but that isn’t necessarily a plus point from the standpoint of rider satisfaction in this class of sports motorcycle. Our Honda had more tingly vibration though the footpegs than we remembered experiencing with last year’s model; the balance-shafted Kawasaki on the other hand is a paragon of smoothness for an inline four. On the somewhat academic question of top speed, our Honda didn’t want to redline in top on the road and struggled to pass the 125mph mark, whereas the GPz sailed into the red zone with ease, posting high 130s in absolute comfort. The Honda’s reluctance may have been a function of its relatively low mileage (just over 1000 miles on the clock at the start of the test compared with the Kawasaki’s 3000-odd), but even fully loosened up we doubt that it would catch this particular Kawasaki. The Honda is over £200 cheaper than the GPz though. The question is, is it only £200 worse than a Kawa?

HONDA CBX750F
£2859 including all taxes

PERFORMANCE
Top Speed -135mph (see text)
Fuel Consumption -Hard Riding -30mpg Cruising -43mpg

POWERTRAIN

Air-cooled DOHC 16-valve, inline four with hydraulic tappets. Capacity 747cc.
Maximum power (claimed) 91bhp at 9500rpm. Maximum torque (claimed) 51.35ft/lb at 8500rpm. Bore x stroke 67 × 53mm.
Compression ratio 9.3:1.
Induction by 4 × 34mm CV Keihins.
Transistorised pointless ignition with electronic advance. Four-into-two exhaust with balance pipe. Wet sump/oil in frame lubrication.
Wet multi plate ‘one way’ clutch.
Primary drive by gear.
Final drive by chain.
Six-speed transmission.

CHASSIS

Duplex cradle frame, air-assisted telehydraulic forks with one-sided TRAC anti-dive, air preload and three-way damping adjustment.
Pro-Link monoshock rear with three-way rebound damping adjustment.
Triple disc brakes with twin-piston calipers.
Wheelbase 57.7in.
Seat height 31.3in.
Ground clearance 5.7in.
Dry weight 4801b.
Dunlop tyres 110/90 V16 (front), 130/80 V18 (rear).

PARTS BIN
HONDA CBX750F-E
All prices include VAT

Fairing (three part plus screen) £131.13 for each side of main body, £34.47 for central grill, screen £55.95,
Undercowl (also three part) £18.14 complete,
Indicator assembly £13.48.
Indicator lens £10.94.
Forks. sliders and stanchions £254.62 per side,
Front mudguard £57.13.
Front wheel £187.79.
Tank £163.24.
Seat £184.33 for complete assembly.
Silencer £119.99 for each side including two downpipes.
Gearlever £11.25.
Brake pedal £28.03,
Footpeg £20.46.
Headlight assembly £144.70 complete with brackets and mounts for both lights,
Brake lever £3.99,
Sidepanel £44.82.
Alternator cover £40.09.
Piston £11.50.
Conrod £57.17.
Head gasket £22.98.
Crankshaft £511.96.
Clutch, complete set of plates and springs £90.38. CDI ignition unit £136.39.
Drive chain £52.10.
Front sprocket £7.99.
Rear sprocket £17.49.
Oil filter £5.30.
Battery £32.29.

SuperBike Magazine – July 1985