Honda CB900 FZ Road Test

Dec 1979

Honda's sixteen-valve 900 has been billed as something special. So we arranged a slightly special test for it. As it is derived from the successful RGB endurance racer, we ran one in our 24-hour test reported in the November issue. But what counts is how it behaves on the road, so we took the same bike, fresh from its circuit thrashing, and put it through the rigours of our usual road tests.

After the 24-hour test, the machine went back to Honda UK for servicing. They were just as interested as we were in the final state of the 900 and completely stripped it to check for wear and damage.

During the test, the bike had lost fourth gear, the front mudguard had detached itself and the bike suffered minor damage in a crash.

A new mudguard was fitted, using bolts instead of rivets and, as this wasn't a unique happening, we understand that Honda will be fitting a more reliable mounting.

The stripdown revealed that the fourth fear cogs and selector were badly worn, here were also signs of wear on third and fifth gear components, although this could have been caused by the need to shift straight from third into fifth after we lost fourth. Third, fourth and fifth gears were replaced, along with the selector forks and drum.

Valve clearances were checked but did not need adjustment, although the cam chain tensioneer had to be reset. Nothing else needed attention. On the cycle parts, the air cleaner element was replaced and the steering head bearings adjusted.

After servicing, someone noticed that one of the front fork oil seals was weeping so they were changed as well — only Honda didn't have any spares for the 900 and seals from another model had to be used. Even if it was only a temporary hold-up in spares supplies, that isn't a \ery good recommendation for Honda's parts department. And wouldn't it be in Honda's interest to use the same seals (along with a stack of similar, fast-moving components) on all of their big bikes?

The gearbox problem was the bike's only real blemish and, considering the level of the 900's performance, it came through the long-distance track test very well.

Mechanically, it is a fairly refined unit although it doesn't give much more power than other bikes in the one-litre class. What is an immediate attraction though, is the well thoughtout layout. It makes the bike comfortable and easy to use in any condi­tion from meandering around at lowly speeds right up to using the full force of the 901 cc motor.

The seat to handlebar relationship is par­ticularly good; it gives maximum use of all of the controls with minimum effort. This leads to a riding position which gives the rider just the rignt poise for confident low-speed control and, as the speed goes up, allows a progressive crouch against the wind. From walking pace right through to getting flat on the tank at maximum speed, it makes the CB900 one of the most comfortable bikes around.

The footrests were in the right place, but the deeply grooved rubber was too flexible; a more rigid structure would feel a lot better. My only other complaint was that the gear lever, although it is fully adjustable on its remote linkage, was too far away from the footrest.

We had track-tested the bike at maximum effort and found virtually nothing to criti­cise. The front brake was very powerful and with massive weight transfer under heavy braking, the back end got so light that the rear brake could be too fierce. Under nor­mal road use, the 900 was slightly under-braked at the back. There's no way around that problem because a more efficient brake would make the wheel lock up too easily during hard braking; reducing the back brake's efficiency would only make things worse for normal use.

Under touring conditions, the tyre wear showed a vast improvement over what we had seen at the track. On tyres which were about half-worn, 500 miles of road use removed only 0.2mm from the back and, oddly enough, 0.4mm from the front. That projects quite a reasonable tyre life in view of the bike's weight and performance. But, in practice, the tyre's life is cut short. As the tread depth got down to 3 mm — about half of the as-new tread — the handling began to go off.

The most obvious sign was the way the bike started tracking over any surface ridges. And there was also a sensation of the front tyre squirming when the machine was heeled over in a slow turn.

This was on the Bridgestone tubeless tyres which had worn slightly faster than the Red Arrows during the track test. Although the Red Arrows gave better grip, particularly in the wet, they allowed high-speed weav­ing once they had worn and the Japanese tyres kept this tendency under more control.

Handling, under all conditions, was positive, with a firm yet light steering. Ground clearance was no problem for our purposes, the footrest scraping down first. But immediately after the footrest goes down, the right-side engine cover touches the ground. Ours was lightly grazed but it has caused bigger problems for some produc­tion racers and not only in the physical restriction on cornering. They are associating the scuffed cover with generator failures — the cover and stator apparently deform­ing enough to let the stator coils touch the rotor.

Although there are six combinations of bump and rebound damping.on the rear springs the suspension seemed too hard for 60mph riding along typical country roads. On smoother main roads, or at higher speeds, it was just right. I suppose that it is another of those compromises which can­not work well under all conditions. What would give a comfortable ride at 60 mph would probably be far too sloppy when tne bike was used to close to top speed.

And, at 60 mph, the 900's engine is almost shut right down. This also accounts for its poor fuel consumption; at most road speeds the rich, idle mixture is still having significant effect — but whatever the reason, the 900 didn't want to go any better than 40 mpg. Deliberate attempts at riding slowly and gently gave us 36 mpg. The best tankful, at 40 mpg, was used mostly in 70 to 80 mph cruising and included 20 miles-worth of full throttle testing at MIRA. At full performance, the consumption dipped to 22 mpg.

The result was that the range of the main tank was rarely more than 130 miles and was often closer to 110 miles. On what would otherwise be a good, effortless touring bike, this is one feature which cries out for improvement.

With a steady 80 bhp available, spread over a band of 1,500 rpm and a long, flat torque curve, performance is no problem. It seemed that the gear ratios were spaced too far apart — for full performance or even for ordinary road use, the bike would be that much sweeter to ride with a close-ratio box. And after the gearbox had been overhauled, gear selection was slow and clunky.

Actual flexibility was quite remarkable. The 900 could be ridden down to 1,000 rpm in top and still pull away, taking anything up to full throttle just as quickly as the rider cared to feed it in.

During the performance tests at MIRA it poured with rain, although this didn't pre­vent the 900 from running a standing start quarter in 12.7 seconds. What it would do in the dry is anybody's guess, but it would have to be substantially better. The rain seemed to have a greater effect on top speed. We were looking for 130 mph or maybe more, but the first two runs were only just above 120. On the next run, the Honda picked up a groove in the surface and turned itself sideways as it went through the lights — at 119.8 mph. With a few violent wobbles it straightened itself out and the next time round it managed 125 mph. It quite obviously wasn't going to go any faster and the tyres, down to about 2mm of tread, were having a hard time coping with the heavy rain.

The overall impression of the CB90 is that it is more than just a performance machine: it is a highly usable performance machine. It fits equally well into the sports or touring categories, is very well thought out and particularly pleasant to ride.

Competition is fierce in the big bike class, and the 900 is quite reasonably priced for what it offers. Most Japanese machines are shaved down by their production engineers until there is little room for error. The big performance machines will be the first to show whether too many corners have been cut.

We noticed signs of weakness in the test model and on other machines. Points like the mudguard failure and engine covers which seem rather flimsy. The field coil brushes failed on our motor and we've heard of one of two alternator failures plus coils which seem to be barely adequate. There are also extra stresses in using a four-valve head — if extra power is extracted as a result. We've seen one machine which has cracked its head, along the casting joint where the twin ports divide, and heard of others with similar cracks. Whether it is simply the way they are made or whether it is likely to cause a mechanical failure are open to debate.

These points will probably not cause trou­ble on a bike in normal use; but they do suggest that the bike has been developed and whittled down until its components are only just up to the job. While they are doing this job they do it wonderfully well. On!y time will tell if there's anything left in reserve.