The neighbour had been running a very tatty Kawasaki Z400J four for a couple of years. He didn’t seem to do any maintenance just rode the bike to work and for long weekends. When his wife became pregnant he put the bike up for sale in MCN at £500. The punters who turned up took one look at the heap and did a quick runner. Eventually, he tired of paying for adverts and told me to make an offer. I looked the machine over and could see that the chassis had some potential, a slight crash a year before meant he had fitted a Z550 front end and there were a pair of Koni shocks out back. The bearings seemed OK despite the fact that the bike had been in need of a good clean for the past year! The engine, though, was a real noisy bugger, with a light fog of smoke out of the Motad four into one, itself in reasonable shape. The Metz tyres were only a 1000 miles old whilst the chain and sprockets were about half worn.
A quick blast around the block revealed the chassis was OK but the motor was well gutless. I thought a hundred notes was a fair price as it seemed the mill would soon need some serious attention. The owner's reply is not printable but we eventually agreed that four fifty pound notes would be fair, all things considered.
I then proceeded to ride around for the next six months and 13000 miles with no engine problems, much to my neighbour’s annoyance. I'd quickly covered the bike in Gunk and jet-washed off all the accumulated grime. The bike was heavy for a 400, as big as most 550s, and the engine was gutless at low revs, needing to be thrashed through the gears. Top speed worked out at a 100mph, reasonable considering the neglected state of the engine. The bike cleaned up quite well, polishing and touching up the chassis over a couple of weekends. I even cleaned the oil off the engine, it was leaking out of the head gasket. I tightened down the head bolts but it made hardly any difference, I had to keep putting in a pint of oil every 150 miles. I didn’t bother with oil changes and god knows how old was the oil filter, it looked corroded in.
Meanwhile, I'd picked up a crashed GPz550 for £600, a three year and 9000 mile old bike. The forks, wheels and frame were all mangled beyond repair. Even the engine had a crack in one outer casing. It took a while to cut away the mangled chassis, but once free I was able to repair the casing with Araldite. I was a bit miffed at the way some of the engine screws broke off when I tried to remove them, but eventually managed to drill them out and re-thread the holes. A large pile of essential electrical bits were also liberated from the wreck, but that was about the extent of its usefulness.
Readers will have guessed what was about to happen. I was going to fit the hot-rod GPz550 engine into the street sleeper Z400 chassis. The engine went in without too much hassle, although some of the engine mountings had to be modified. The chain didn’t line up either, but it wasn’t so far out that a bit of bodging couldn't be employed. Much more of a problem was fitting all the 550’s electrics into the 400’s loom. Nothing much matched up and the bike was off the road for a whole week whilst I fumbled my way through the mess of wiring. The Z400 featured a non-standard rectifier that had the wiring altered to suit.
Not content with this major feat of engineering, I'd also decided to lighten the chassis, drilling holes in minor brackets, junking the indicators, mirrors and centre stand. Skimpy plastic guards and a home-made seat with a GRP base finished off the effort. Don’t know what it weighed, though, I didn’t fancy trying to perch the beast on the bathroom scales. Flat bars and rear-sets were also fitted in deference to its new found turn of speed. Luckily, the Motad fitted on to the 550 engine with a few large taps from the hammer.
When the beast was. finally sorted I breathed a sigh of relief and pressed the starter button. A 4000rpm tick-over was hastily cured by rerouting the throttle cable. After that it was smiles all the way. What a performance transformation. The new motor put out about 65 horses, more than twice what the old, worn 400 was managing. That, and the lightened mass, meant it would now rear up on the back wheel on enthusiastic take-offs and roar up to an indicated 130mph. This kind of speed gave pause for thought, as the once somnolent chassis suddenly found itself bouncing about at an alarming velocity, neither the forks nor brakes were able to cope, and the swinging felt like it was about to fall off. When I found that the swinging arm bearings were all but shattered, I coughed up for one of those neat alloy swinging arms. The first one they sent didn’t fit but the second attempt was OK after I‘d put in a couple of spacers. This beautiful piece of work had eccentric adjusters at its end which simplified chain adjustment - just as well as the new power stretched the cheapo chain at about three times the rate of the old motor. A beefy fork brace was attached out front and a set of tyres finished off the job.
Ah, that was better. The bike was stable up to 110mph, then started wallowing a bit but not so bad as to make you want to back off. I could scrape the bottom of the Motad in wilder bends and make the back tyre hop a couple of inches if I opened up in third or fourth when leaned over. Although there was a definite power band, between 2000 and 6500rpm there was much more torque than on the 400. The bike would run along quite happily in a tall gear at low revs. I’d had to rip out the old air filter and fit K & N‘s, so the freer breathing may have helped.
I was rather surprised to find that economy had improved from 40 to 45mpg on the 400, to an astounding 60 to 70mpg on the bigger engine. It was dead easy to average 65mpg, sub 6500rpm riding guaranteeing nearer 70mpg. Admittedly, the 400 was worn whereas the 550 was nearly new, but I suspect the long model life and slow evolution of its two valves per cylinder design had paid dividends. Interestingly, the GPz was always touted as the sportster of the range but had always managed better economy than the plain Z550 or rugged GT550. It must surely have the most efficient cylinder head design of the old fashioned air cooled fours!
This opinion was emphasized by a couple of hours test riding a 550 Zephyr. I loved its looks, but it was heavier, slower, less punchy and poorer on fuel than my dear street sleeper. Kawasaki had changed its cams, valve timing and ignition to give it a wider, milder power band but somewhere along the line had choked off the essence of the engine. Its one real improvement was smoother running, both in terms of vibration and transmission lash. My bike lurched into gear and made protesting noises when I used the box in anger, whilst there was an annoying patch of vibration between 5000 and 7500rpm. The latter may merely have been a mismatch between frame and engine characteristics or an inherent malady within the motor.
I rather enjoy this street sleeper lark. I can can saunter up to the lights on the bike, take the looks of disdain from the plastic fantastic brigade, and stomp on them up to about 70mph. With my modified seat and riding position, the bike is just as at home droning down the motorway with a ton plus on the clock or cutting up country corners. Sure, the bike has none of the gloss of the new retros, but I like to think that it proportions lend a sense of function to its plain black appearance.
Yes, it has the usual caliper problems, the wiring rots away as fast as I can patch it up (spare fuses are essential accessories) and the consumables wear out in the usual disgusting manner. The motor’s incredibly tough, can take massive neglect of carbs, valves and camchains like few other engines. The ignition black boxes will blow up if their rubber mountings are allowed to decay, but the alternator and rectifier last much better than Suzuki items. Overall, I think my bike's as neat as any other machine costing less than a grand. I expect to keep it for quite a few years.
Kevin Connoly