Kawasaki Z1B/R

Roy Mayne held nothing back when it came to sourcing the best bits for his fast and far from stock Zed

It's fair to say that Roy Mayne prefers a good special to a classic restoration. “One of my mates restored a Z1 – he phoned me up halfway through it saying, ‘This is so boring,’” laughs Roy. “I’m not sure I’d go that far but at the end of the day a resto is just following a catalogue – I love how people are saving these old machines in their original condition but building a bike like mine is a much more involved process.”

The bike Roy is referring to (and lovingly patting as he speaks) is a 1975 Kawasaki Z900. Well, at least some of it is. “Specials are all about the details and making sure you get the lines right,” he says. “I definitely took influence from AC Sanctuary’s work in Japan. I actually packed up biking back in 2001, but I turned 50 last year and decided I wanted to get back into it. I’d owned loads of bikes in the past, but coming back to it I knew I didn’t want a modern Ducati or R1 – I like tinkering around in the garage and I wanted to build something different. That’s when I remembered the Z900. I was about 10 when it came out – I lived around the corner from a Kawasaki dealership and I used to see them all the time. I suppose I never forgot them.”

Despite having previously stripped down and modified a GSX-R1100, and made a race-style special with a 1998 GSX-R750, Roy’s 15-year absence from biking soon taught him a valuable lesson: prices of any ’70s Kawasaki have gone absolutely mental. After a few months of internet mooching he finally arrived at the bike that would soon turn into the one you see on this page – a 1975 Z1B/Z1-R hybrid the condition of which was, to paraphrase Roy, like a pile of something steaming and brown.

“It hadn’t run for 10 years and was a complete dog – but it still cost me three grand,” he laughs. “That said, it already had the monoshock conversion and the front-end mods done, so a special of some sort had been started.”

Roy had, in fact, bought one of those projects that someone had begun but not been bothered to see through, yet further Poirot-style investigation revealed more intrigue about its past. “I knew from the paperwork that some of it had been built by a bloke in 1990, because I had a piece of paper to say that the monoshock conversion had been inspected by an engineer. A few things had been drilled for lock-wiring as well, like the filler cap, so I think it had been raced.”

Roy’s first job was to get the bike running – a task made trickier by the fact that there were so many burnt-out wires it all looked like a really unappetising plate of hideously over-cooked noodles. Once he’d replaced all the necessary cables it spluttered into life and even ran – despite smoking like a ’70s clubland comedian and sounding even worse. Even so, the engine had received some major surgery in its previous life, and Roy’s first priority was to enhance it.

Taking the engine apart, Roy was looking at a motor that had already been bored out from 903cc to 1015cc and treated to a gas-flowed cylinder head and Russ Collins Pro-Stock cams. “It needed a rebore, so I took it out to 1030cc,” says Roy. “That’s as big as you can go with standard Z900 liners – I had to have new pistons machined with bigger cut-outs so the valves didn’t clatter them. I also fitted new shims and buckets from a 1983 GPz1100, which go straight in.” The final touch were the Keihin CR33 race carbs, replacing the CVs that were on it before. “I bought them secondhand online,” smiles Roy. “They were really worn so I rebuilt them with all-new internals.”

Taking what had already loosely been started with the engine and developing it has been something of a theme with this bike.

SPECIFICATION
1975 Kawasaki Z900

ENGINE 1975 Kawasaki Z1B, air-cooled, dohc, inline-four, bored to 1030mm with machined cut-outs to pistons, skimmed and gas-flowed head rebuilt with APE bronze guides and seals, triple angle cut valve seats with under-bucket shim conversion from 1983 Kawasaki GPz1100 Uni-trak. Russ Collins Prostock cams, all camchain, rollers and guides replaced with APE/Liska race-spec parts, APE low-level breather, APE kickstart blanking plate, 13-row APS oil-cooler with KipKawa manifold, stainless braided lines and anodised fittings with modified HEL performance bracket, Keihin CR33 carbs with billet anodised velocity stacks, Dyna coils, Taylor HT leads, Delkavic exhaust headers modified with new collector to fit Dan Moto end-can and link pipe

CHASSIS 1978 Kawasaki Z1-R, braced and monoshocked with 1990 FZR1000 Exup swingarm and wheel with 170-section Michelin Pilot Sport, all superfluous brackets removed, all welds smoothed and powdercoated satin black, Nitron NTR R1 shock, Talon alloy rear sprocket and Tsubaki gold race chain, AC Sanctuary chain tensioner roller, rebuilt 1990 Yamaha FZR1000 Exup forks with new seals and bushes. Powdercoated sliders and rechromed and titanium-coated stanchions, billet slab yokes, 1990 Yamaha FZR1000 Exup front wheel and mudguard with 120 section Michelin Pilot Sport, Blackshadow 320mm wavy discs with 2003 Yamaha R1 goldspot calipers, under-slung rear caliper conversion from a Yamaha Thunderace, bespoke torque arm and paddock stand bobbins, all caliper, sprocket, disc, torque arm and chain adjuster bolts made from Grade 5 titanium, new headlamp with billet alloy brackets, Tarozzi rearsets, PMC seat

THANKS Ian Giles for the bits he made, Neil Laffling for the bits he got me, Ian Padley for the advice and long-suffering wife Melanie for putting up with it all many of the ideas were already in place but simply fell by the wayside with an owner who lost inspiration. “The 1978 Z1-R chassis was already there, as were the wheels, forks and swingarm which were from a 1990 Yamaha FZR1000,” explains Roy. “That’s not to say all this stuff was finished by any means. Everything that’s black has been shot-blasted and powdercoated. All the nuts and bolts were replaced with stainless steel ones. The discs, calipers and sprockets now have titanium bolts. It’s a bit self-indulgent but then it’s a special, isn’t it?”

Details are everywhere you look on Roy’s Zed. The low-cut PMC seat keeps the AC Sanctuary look going, while the rear indicators were bought from Japan in a bid, Roy says, “to get away from all those silly little LED ones people have.” Even the standard rear light has been lifted and mounted inside the rear-end so it sits flush. “That took a couple of days to get right,” smiles Roy. There’s even a genuine AC Sanctuary part on it. “It’s a chain tensioner,” he says proudly. “It’s only the size of a 10p piece and you can’t even see it, but it still set me back a hundred quid.”

The finished article is a bike that definitely has that AC Sanctuary look Roy was going for – and it runs pretty sweetly too. “Before I rebuilt the carbs I had it dyno’d at 100bhp at the back wheel – not bad considering it only had 65bhp when it came out of the factory,” says Roy. “It’s still a pretty heavy bike but it gets down the road OK.” All in all, pretty impressive considering it was only off the road for six months.

For his next project Roy’s building a 1983 Kawasaki GPz1100 Uni-trak from the ground up, which promises to be another belter. “I’ll keep the details a secret for now but I’ll be in touch when it’s finished,” he grins. Any clues to the direction he’s going in? “My lips are sealed. But I will tell you this: it won’t be a classic restoration…”
 

IF A JOB’S WORTH DOING...

Thunderace rear caliper took (literally) a month of Sundays to measure-up, modify and fit to perfection, but the result is precisely as Roy wanted. When it’s your special, have it your way.
 


THE HEIGHT OF QUALITY

Nitron shock, always one of the higher end options when it comes to rear springing. Roy raised the rear ride height by a substantial 45mm and the machine’s stance is now spot-on.
 

OIL BE BACK

“I added an oil-cooler as well as this nice little KipKawa ally forged manifold. It was another expensive part, but sometimes you buy the best you can get rather than the best you can afford,”said Roy.
 

FRONT-END

Achieving the right look for the front of the bike also required some jiggery-pokery. “The light is just a generic one off the internet, but when I fitted the Renthal drag ’bars the clocks looked a bit too high,” explains Roy. “I really wanted to keep the original ones, but to make them look right I had to make a couple of brackets so I could move the clocks forward and drop the headlight down the forks a bit. An inch here and there makes all the difference.” Roy’s gone to town on the 1990 FZR1000 forks. “They’re nice, chunky 43mm numbers which are thicker than the stock ones – I’ve had them re-chromed and titanium-coated. I didn’t want usd ones.”
 


PAINT

The standard Z1B bodywork has all been resprayed with Roy’s unique vision in mind. “The lines pay tribute to the bike but are a bit different – Race Paint UK in Nottingham did a top job.”


BEST BITS

Having stripped the motor down before having everything shot-blasted and the casings polished, Roy decided to treat himself to a few saucy parts. “I had to replace the camchain sprockets, so I got some APE Liska ones – they’re the best of the best. They supplied all the guides and rollers as well – they’re painfully expensive. The seats have been triple-angle-cut and there’s also been an under-bucket shim conversion. It’s fair to say I’ve gone to town on the engine.”

PIPE WORK

Replacing the dreadful exhaust that the bike came with was always a top priority. “I basically bought a set of Delkavic headers and a Dan Moto end-can, took it into a local exhaust specialist near me and got them to join it all up,” says Roy. “I knew how I wanted it to look but I’m a fridge engineer by trade – welding isn’t my strong suit. I fitted it to the bike but then decided it was too long, so I took another three inches off it. I might even take a smidgeon more off. I’m a bit OCD…”

BUSY ROUND
THE BACK

“The rear brake is originally from a 1990 Yamaha FZR1000 Exup. I wanted an underslung back brake so I modified a Yamaha 1000 Thunderace rear caliper and hanger – that took a lot of measuring. I had to make a spacer, then cut the bracket on top and have it welded underneath for the torque arm to convert it to underslung. The swingarm took about a month. The FZR rear shock was then replaced with a Nitron one, and I’ve also jacked up the back-end by about 45mm.”