Kawasaki were, of course, very well aware of the fact that two pistons moving in unison were going to create plenty of primary vibes due the inherent lack of balance. That's why they added a chain driven balance shaft to counteract these vibrations. While such a balance shaft can cancel out the forces of pistons at certain points in the combustion cycle, the shaft, itself, does nothing to balance it other points in the cycle. Thus the elimination of vibration is impossible in such a situation. Throw in some wear to the extra components such a system employs and there's more vibration than if the poor old engine was left as just a plain and simple design. If the Kawa doesn't vibrate much as a Triumph 350 or 500 twin it is because it has a better engineered engine, with a proper four bearing crankshaft and an OHC design less affected by whatever nastiness the engine produces. The Z400 has vibration levels little better than the XS650, which can be considered the ultimate in straightforward design.
The simple solution to the vibes is to have the pistons moving up and down alternatively. Perfect primary balance is produced at the expense of a torque reaction along the crankshaft that would do very nasty things to mere two bearing cranks employed in British twins, but produces a much smoother engine in such devices as XS400 Yamahas and old CB450 Hondas. Suzuki also use this option in GS400/425 engines when they remove all sensation from the engine by the silly provision of a gear driven balance shaft. Honda, a long time advocate of 180 degree cranks, copied Kawasaki in their Superdream series to produce a powerful engine that could self destruct when neglected.
Having wasted a huge amount of space and time complaining about the awful engine design, I now have to admit that the Z400 is a jolly pleasant bike to ride. Not fast or economical, you understand, but the kind of bike that's easy to get along with, feels reasonably secure and never intrudes far enough to cause complaint. It has a little bit of character without all the trauma of cycle and engine parts leaving a messy trail of debris or the need to pack a box full of spare parts. Of course, the Kawa is no tool for street hoodlums - all of the bike's performance parameters rapidly begin to fall apart once the extremes of power and handling are encountered, but then there are a whole host of interesting middleweights that offer much more high speed insanity. The Kawasaki makes no pretensions towards being an out and out hustler and thus can, I suppose, be forgiven when it objects to such abuse.
The Z400 is an update on the KZ400, a design basically identical except for an extra gear and some minor mods to the engine that helped sort out the earlier bike's penchant for self destructing just after the end of the guarantee period. The Z400 was superseded by the Z440, which except for its higher selling price, is a much more useful and economical device.
But let's get back to the Z400. The engine developed the far from startling sum of 36hp at 8500rpm from a mere two valves per cylinder, operated by a single overhead camshaft via a set of rockers with screw and locknut adjustment that didn't need adjusting very often. Kawasaki had the decency to use long lasting, maintenance free gear primary drive (but then so did all their rivals) and a light but strong multi-plate clutch. Given the large dollop of mid-range grunt, use of a six speed box could easily be condemned as exceedingly silly, but it was easy enough to use and didn't fall apart at the same rapid rate as the five speeder fitted to the KZ. Given thirty grand on the clock, missed changes between first and second and difficult neutral selection are quite common. With forty grand on the clock, gear selection is a carefully planned action but the box has enough feel to it to let the rider compensate for wear.
Out on the road, the Kawa is happy enough to be stuck in fourth or fifth and can be used from between 25 and 85mph with hardly any complaints.Trying to go any faster wasn't a pleasant experience. Excessive vibes fron the engine start to affect petrol tank, footrests and handlebar grips. While this was a mere inconvenience at lower speeds and revs it quickly becomes rather nasty. Triumph twin owners could probably grin and bear it, but it's much worse than the secondary vibes from straight fours of more than twice the Kawa's capacity and power. At 90mph, by comparison, the sixties CB450 was alive but unconcerned, the GS400 was still electric smooth, the XS400 was beginning to throb a little and the CB400 was marginally smoother than the Kawa.
Pushing beyond 85mph also upset the Kawa's handling. Weighing well under 400lbs meant the Kawa should not have caused too many problems for either chassis or suspension, but the front forks and rear shocks with eight years and forty thousand miles of abuse, were lacking in both damping and springing. The result was a slight weave on flat straight roads, that became worse as speed increased, until when flat out at the ton the bike could require a car's width of road in order to survive. Throw in some bumps or worn tyres and speed wobbles are a natural result. It was easy to trip up the suspension when chucking the bike through sane fast, bumpy curves - the Z400 exhibited all the attributes of a NSU Quickly with a bolt or two loose when any attempt to really thrash the poor thing was undertaken. At least the Kawa could be relied upon to give some kind of warning and some degree of feedback before it acted out its suicidal urges. The Superdream led the pack as far as handling and ride went, closely followed by the Suzuki (lacking in feedback) and the Yamaha (quick rot suspension and dodgy swinging arm bearings). The Kawa ends up not far behind the Suzy, especially for those who don't travel too fast and like to know how the tyres are reacting to the road.
At legal speeds the Kawa is perfectly acceptable. It feels very secure and its light weight make it a piece of cake to flick through heavy traffic and along country lanes. At these lower speeds even worn tyres and bumpy roads can be taken in their stride. As most of my riding seems to be done in wet weather, I was off quite happy to be pottering around on the Z400 in the wet, when I had no intention of speeding and needed only a bike that held no unpleasant surprises and wasn't likely to flip its wheels suddenly. The ability to stick it in one gear and control speed by the throttle was a welcome relief from some of the brutal devices that come my way, when touching the throttle often has the thing trying to spin the back wheel, and forward progress is a series of frightening lurches. In this department the Kawa beats the rest of its rivals.
It's a pity I can't extend such praise to the front brake. It's not the worst disc I've ever had the pleasure of using. It can be used with a great deal of impunity when braking in bends and it doesn't suddenly lock the front wheel without any warning. This is probably because it doesn't have very much stopping power. I shall refrain from spending this paragraph in extolling the virtues of decent drum brakes - by now you should have heard enough of my discontented mutterings on this subject - and concentrate on illustrating the silliness of 1970s disc brakes. The brake pads last for about eight thousand miles, or if you prefer to combine danger with disturbing screams from the front end of the bike (if not alarmed pedestrians) they can be taken right down to the metal after ten grand. As the latter course leaves some badly scored discs this could turn out rather expensive. A set of pattern pads that further impair braking ability can be found for around ten quid. An amusing hour can be spent screaming obscenities at motorcycle designers, next door's cat and local yobs while attempting to replace these pads without becoming a hospital patient. This is on a lucky day. Given a few thousand miles of winter riding, then the completely exposed and perfectly placed calipers will pick up all kinds of interesting pieces of grit that will seize up and corrode the brake. This is true of many bikes, but the Kawa suffers the faults without returning the kind of braking force that can be expected from a decent drum tens years its senior. I 'm only surprised that I don't see Z400s with heavily vandalised front ends...
While I'm in a bad mood I may as well go for the jugular by mentioning fuel economy. Oh dear, oh dear, I can't quite find the correct adjective to describe the way the Z400 consumes fuel. If I was being kind, I could compare it to the equally slow (ho hum) latest Honda CB350S. The Kawa would just about survive comparison. If I was being really nasty I could compare it to the much faster and older CB450. The Kawa would be shown up for the appalling engine design it really is. While the 45hp CB450 can average 70mpg , the poor old Kawa is hard pressed to better 50mpg even under the moderate use its chassis and engine confines its rider to employ. I managed to restrain my right wrist for long enough to find out the economy when pottering between 30 and 40mph, and was shocked to get just 60mpg. Cruising at 70mph returned 48mpg, thrashing the engine at the limits of revs and vibes returned 35mpg, although the latter figure has little relevance as such speeds can't safely be maintained for any length of time. Even if I confine myself to comparison with bikes of the same era, such as the Suzuki GS400 , the Kawa still loses out by a large margin. Blame that balance shaft, and the use of twin carbs in such a low power unit. The later Z440 develops more power and consumes less fuel.
Before Z400 owners tear up this magazine in rage, I'd better throw in some good news. This sentence has just closed down my brain. Good news? Ah yes, rear tyres. They seem to last for quite high mileages, someone's even claimed 15000 miles from a Roadrunner , but twelve grand seems a more representative mileage. The front goes for an extra few thousand miles. Even chains make it past twelve grand with ease, and well maintained jobs have almost done twenty grand. Oh yeah, the thing even looks quite neat in a classical way, stands out rather in these high tech days , the way all those British twins used to make Jap multis look so crass back in the seventies. But we all know that looks can deceive, don't we? The paint on the cycle parts is pretty good stuff, comes up quite well with bit of elbow grease. The frame's paintwork isn't so resilient; I seem to recall a friend's bike was spotted with rust after a mere two years. Chrome is in trouble after three years. Exhausts last a similar period before giving in to nature Engine life varies to such an enormous degree that I'm hard pressed to give any coherent information. This is probably nothing new.. try fifteen grand for something that's been thrashed and neglected from birth, 25000 for a bike given moderate treatment and maintenance, and about 45000 for the ideal owner who never breaks the speed limit and has swapped religion for bike maintenance. Any number of problems can cause mechanical mayhem rings, tensioners, valves, crankshafts, balance shafts... take your pick.
The Z400 only makes it as a very cheap hack. Try tuning the engine, it'll fall apart. Try uprating the suspension and you'll have to thrash the engine to make use of the new handling abilities, which will also make it fall apart. Use it as a slow commuter and you might lucky and get years of reliable service. But then you'll be suffering the same fuel consumption as larger bikes.