HONDA CB900F

Story by Ben Wilkins for Classic Motorcycle Mechanics

The CB900 has always played second fiddle to its CBX1000 big brother. But this was Honda’s production racer for the biking masses...

If ever a bike has lived in the shadow of another it’s the Honda CB900F. When the CB900 was launched in 1979 the press, and public alike, had their attention firmly fixed on the headline grabbing six-cylinder CBX1000. 31 years later it’s still the CBX that is the bike most fans of big Hondas favour. But with prices of CBXs occasionally crossing the £10,000 mark they’re now the preserve of those with serious amounts of cash. Just looking through the classifieds in CMM though you can pick up a tidy standard CB900F for less than £1000 and a tastefully modified CB900 Spencer replica could be yours for less than £3000. That’s far more easily within the reach of the majority of 70s muscle bike fans. And despite the common perception it doesn’t mean you’re getting a second rate bike. Honda certainly didn’t think so...

It’s commonly thought that the CB1100R was Honda’s first production racer but that wasn’t until 1981. No, the CB900F was launched in 1979 with Honda’s corporate eye firmly on a new class of racing. In 1980 a new racing class was launched for production based machines – AMA Superbikes.

The regulations for the new production class stipulated that the racing machines have the same number of valves and carburettors as the production machines they were based on. Honda’s RCB endurance racers were the inspiration for the CB900F. With experience gained from the RCB, Honda were confident they could tease enough power from a four-cylinder engine and, besides, the six-cylinder CBX1000 motor would be too wide for serious racing. Pedigree doesn’t get much better than that.

High tech motor

Technically, the CB900 was a revolutionary engine. It was needed to be narrow for racing so the design was based around the CB750 bottom end but beefed up in key areas to take the extra loads that would be going through it. The top end features a four-valves per cylinder design, which lends itself to racing use; four lighter valves will rev faster with more reliability than two larger and heavier valves. And this is an engine that thrives on revs. Peak torque is at 8000rpm and peak power is delivered only 1000rpm later. Another aspect of the four-valve design is the centrally positioned spark plug. According to Hiroshi Kameyama, a director of Honda R&D at the time of the CB900’s genesis, an important aspect of the central plug is that the length of the flame path is equal in all directions across the combustion chamber giving better overall performance.

A feature of the new engine was the use of a Hy-Vo silent camchain two-stage drive. The exhaust cam is driven directly by the camchain that runs up the centre of the engine, then a second chain from the exhaust cam drives the inlet cam. Honda said the system gave more room for the inlet ports and reduced mechanical noise. But the CB isn’t the quietest of motors because there’s no water jacket around the cylinders to mute the mechanical noise. This was a conscious decision by the designers at the time.

According to Honda they’d been researching and developing air-cooled four-valve heads for many years and they were happy with the technology. We mustn’t forget either that an added bonus of air-cooling is the weight saving over a water-cooled lump – something that Honda naturally considered to be important in a production-based racer.

Riding the CB900F

Firing up the CB900 today is easy. Pull the high-mounted, slightly over-engineered choke lever on the left hand bar, which was something of a novelty on a bike in the 70s because most of them were operated by a plunger situated on the carbs themselves, and press the starter button. The motor fires quickly into life and the tick-over soon settles down to a deep purr through the silencers.

Leaving it warm for a couple of minutes before heading out gave me a chance to look the bike over. The bolt-together alloy wheels give the bike a more futuristic look than the spokes of its contemporaries. The rear suspension units have been replaced with good quality Hagon items and the exhaust silencers have been replaced at some point with aftermarket chrome silencers. That’s all good news.

Blipping the throttle produces a wisp of blue smoke while the engine is still cold but this disappears as the engine warms and the needle bounces enthusiastically around the rev counter. The redline is at a heady 9500rpm – evidence of the 16-valve motor’s ability to rev freely and hard.

At standstill the CB is one helluva motorcycle to move around and it’s one of the heaviest bikes I’ve encountered to put onto the centrestand. There just isn’t enough leverage to easily move the bike onto the stand; I had to use all of my body weight and even then I could feel my back starting to complain. Putting it on there once a week to oil the chain would be more than enough.

Once moving the CB does that nice Honda trick of losing the portly overweight feeling. There’s a slight stretch to the bars over the long fuel tank. As with other bikes of this ilk, the CB has a comfortable yet sporting riding position. The aluminium footrest holders put the pegs in a comfortable position that doesn’t hamper spirited riding and the cast aluminium clip-ons give an upright yet meaningful posture to the riding position. It’d be easy to do big miles on this bike.

The engine pokes out from under either side of the tank giving an impressive and meaningful attitude to the bike. The motor is smooth and docile until 6000rpm at which point it starts to pull strongly, shifting the 250-odd kilo CB along at a decent rate. Keep it revving, using the full force of the 901cc motor and the CB900 is impressively quick. It reached 130mph back in the day and with a fairing and some minor tuning Motor Cycle Mechanics speed tested a CB900 at 143mph.

Even though the motor is designed to work well at high revs, Honda haven’t forgotten about town riding. This is one remarkably flexible performer. Letting the revs drop right down to almost tick-over and then opening the throttle did nothing but produce forward motion. Impressive. Less impressive is the fuel economy. Ridden sensibly at cruising speeds the CB will return around 40mpg. Rev the motor hard, and that’s how it likes things, the fuel economy will only get worse from there.

Thankfully the chassis is up to the performance of the motor. This bike has Hagon rear suspension units that do a good job of controlling the back end during sporty riding but the original units would have been Honda’s Full Variable Quality adjustable units (or Fade Very Quickly as they were called by some owners).

The 70s was a time of experimentation and the front forks on the Honda were complicated ahead of their time. The forks feature air assistance to allow stiffness adjustment in an early attempt at adjustable preload. The forks also feature an anti-dive system that stiffens them when the brakes are applied yet leaves them compliant when riding on bumpy surfaces. The fact the system can still be felt working says plenty about the original design.

Disparate markets

It was at this time in the late 70s that Honda started to develop differently specified machines for the American and European markets. The bikes for the American market were produced with more of a cruising and posing slant to them while the European market, which was demanding good handling and performance, were given sportier machines. The CB900 was one of the models that came specified differently in the two markets with both cruising and sporting versions of the bike being produced. Kameyama was quoted at the time, “Our aim was not to build almighty motorcycles but to find a special design for the enthusiast interested in handling and performance.” The design team were given the brief to produce a sporty look and to include a resemblance to the RCB endurance racers of the previous years. That’s what Minoru Morioka, the bike’s stylist, produced to great effect. The styling of the CB is smooth and flowing – the tail unit being a great piece of design that still looks beautiful today. Maybe not striking in the way of a Bimota or Ducati of the time but striking all the same.

Of course, we couldn’t write a feature on the CB900F without mentioning the most famous CBF of all – Freddie Spencer’s 1023cc CB750F. Spencer came third in the AMA Superbike championship in 1981 and runner-up to Eddie Lawson in 1982. For 1980 and 1981 the bike he raced was based around the CB750 but the machine he piloted to victory at the infamous 1982 Daytona Superbike race was based on the CB900. Honda’s original plan to make a production machine that could go on to win races was more than realised with Fast Freddie at the helm.

Buying

The fact that the CB has lived in the shadow of the CBX for three decades means a CB can be bought for minimal money. We’ve seen plenty going for the £750 mark privately and good condition machines from dealers for less than £1500. The bike in this test is a perfect example. This was originally a Hong Kong market machine and is in a paint scheme we didn’t get on British shores, but it is an original Honda colour-way.

The most important thing is that you get a machine with good bodywork. As with any 70s machine, the bodywork isn’t always easy to track down. The better the bodywork the more desirable the bike.

The main problem these days, as with most older Hondas, is the battery charging system. The first thing to do is check that it is actually charging the battery. A quick connection across the battery terminals with a multimeter with the engine running will tell you if the two-unit regulator/rectifier is functioning. Either can fail. It’s a well-known problem and isn’t expensive to fix.

As with any 70s machine, the electrics will most likely have had bodge repairs over its 30 years life and the inside of switches are likely to be corroded. Start in these areas with any problem electrics.

Due to the engine looking outwardly identical to the CB750F motor you should ascertain that the 900 you’re looking at is actually a 900. It was common for owners to replace a damaged or blown engine with one from the more common 750 to keep their bike on the road. The big clue to engine capacity is the 900 has an oil-cooler and the 750 doesn’t. More than a few owners are riding around on a 750 without realising it. The 901cc engine also meant increased insurance premiums because it put it into the same bracket as the 1000cc and 1100cc machines of the day. Cunning owners ground off the capacity marking on the engine and re-registered them as 750s to get cheaper insurance. So it’s entirely possible to find a CB750F with a 900 motor in it and a CB900F with a 750 motor slotted in place. Cam chain and tensioner issues on early models can partly explain why the CB900 has never developed a big following. They wore quickly and many failed but any bike running well these days will have had them replaced and the problem sorted. Honda fixed the issue on later models. These issues were another reason why the above mentioned engine swaps were popular.

It’s also common for bikes that have been stood for many years to be quite smoky on start up due to the rings gumming into their grooves and not sealing correctly.

Quite apart from being a great bike in its own respect, a bike like the CB900F in this feature could be the affordable start to a cracking Spencer replica. When the Suzuki GS1000 and its other contemporaries are rising steeply in value, a slice of Honda homologation special for less than £1000 has got to be the biggest bargain on the classic market.

The CB900F Bol D'Or. Author unknown.

It is said that racing improves the breed. That could be used as an epithet for the remarkably good handling of the CB900FZ Honda, or Bol D'Or as it is known on the Continent. If its' specification seems a little familiar, that can be put down to its racing parentage, namely the one-litre Honda wonders that have been cleaning up in endurance racing for the past few years.

The 900's evolution is not just a simple matter of racer turned road-burner, however, and in fact goes back to the time when Honda were looking for a new sports flagship. With vast funds available for research and development of new models, the R & D department was given a free rein to develop whatever model they thought fit. Under the watchful eye of Soichiro Irimajiri, renowned for his racing bikes of the 1960s and for his hand in the companys' Formula One car projects, two bikes were developed. Both machines were of one-litre capacity, both had approximately the same performance and both used lots of know-how from the endurance racing project. The only difference between the two models was the number of cylinders they had. One was a conventional four and the other was a six. The six became the CBX and was a shade quicker than the four, sounded different and most importantly, looked different.

Honda, however, had other plans for the one-litre four. It was marketed as the CB900FZ with engine size reduced to 902cc, but only Europe was afforded the pleasure of sampling this model while the United States market had to be content with the similarly styled 750FZ.

The CB900FZ follows the style of the later versions of the 750, but its engine has more in common with the six-cylinder CBX. They share the same 64-5 mm bore, although the 900 naturally has a longer stroke to compensate for having fewer cylinders. Its stroke is actually 69 mm, which makes the unit undersquare, quite a rarity on a modern motor cycle engine. With a compression ratio of 8-8:1 the 900 produces a staggering 95 bhp at 9000 rpm and this no doubt is due to the motor's efficient breathing by way of four 32 mm carburettors, and four valves per cylinder, operated by twin overhead camshafts.

The rest of the mix in the CB900FZ package is quite straightforward with a wet-multi-plate clutch, five-speed gearbox, chain drive, twin downtube duplex frame, conventional swinging arm suspensions, triple discs and alloy wheels. What the specification doesn't say is that the bike has one of the best set-up chassis available on any bike from the Orient and is far superior to the Irimajiri-inspired racing-type diamond spine frame of the CBX. In handling, the CB900FZ is a revelation and it is only at the far end of the speed scale that its manners are anything less than superb. It feels just like an Italian superbike, and that really is high praise indeed.

The CB900FZ is a shatteringly fast motor cycle. It has a top speed of almost 130mph and the roads

on which that sort of speed is attainable are few and far between. Just as impressive is the 900's quarter-mile time of 12.3 seconds, putting it on a par with Kawasaki's KZ1000 and Suzuki's GS1000, both machines sporting engines larger than that of the Honda. In spite of its rocket-like performance the CB900FZ is a highly refined machine with silky smooth manners and the feel of a true thoroughbred. It is true that the CB900FZ is slightly slower than its big brother the CBX but it has two assets the big six-cylinder machine lacks. For one thing the CB900FZ is surprisingly economical,

returning a fuel consumption figure of 40 miles in the gallon. Secondly the 900's handling is definitely superior to the that of the CBX's which makes it a real winner. With cornering power in reserve right up until the bike grounds on each side. Braking is excellent and there is enough power in the engine to keep the whole plot speeding through sharp corners or fast sweepers.

It may seem that in Europe, especially in the top league with the 900 and the CBX, Honda have saturated the market and their models must inevitably overlap. It is not until one has ridden both bikes that the differences are obvious and noteworthy. Unless ridden full bore, there is little to choose. When such realms are reached the CB900FZ has a fine chassis that puts it above the CBX, while the CBX has an engine that is second to none in motor cycling. As that other saying explains: you pays your money and takes your choice...

(Formerly Suzuki gallery)

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