In standard form the Kawasaki Z650 is a perfectly able machine. Its chassis is competent, and the engine willing to rev on, making it the almost ideal B-road scratcher for the late 70’s. However, like most bikes from the period, a standard Z650 does show its age in more modern times and as seen here by choosing a few areas to improve the middleweight Z can be transformed.
Simon’s perfect motorcycle came about by accident in as much as it wasn’t planned and the bike had previously been in a serious incident, effectively leaving it as an insurance write off. The Z650 was given to him the day after the live aid concert on the 14th of July 1985, it was as part payment for work he had carried out on a mates machine and was initially in a bad way and looked to be in a sorry state. There was several parts missing and would have been considered a total wreck by most people, but not Simon. There was considerable damage to the engine with a hole having been punched in the crank casings which was originally repaired with chemical metal, this has since been welded to form a permanent repair, and lots more, not so serious damage. Initially the bike was hurriedly repaired and pressed service as a day-to-day hack.
For the next ten years the bike was used daily and run on a tight budget, then as circumstances changed Simon decide to set about tidying the Z650 up and with this came the idea to improve the bike in some areas. Once inside the engine other concerns were revealed, a cylinder head that, once apart showed signs of the dreaded stripped cam cap threads, a common fault on this and a few other Kwaks, and one that is easily fixed if dealt with straight away, however these had been ignored and the damage was way beyond repair. A new cylinder head was purchased from a nearby breakers and it was only once back home that it was realised a Z750 head had been given to Simon instead of the correct but similar looking Z650 item. This in turn started the brain working and soon a set of barrels and pistons were acquired to keep the 750 head company. With an extra 4mm of bore to squeeze into the B1 bottom end the mouths of the crankcases needed opening up to allow the bigger bore barrel to slide into place, and with that job done the engine capacity instantly grew in size by around 15%. By now the idea of ever restoring the bike back to its original status was long gone and Simons brain was allowed a free rein to start creating a bike unique to his needs and desires.
A set of 34mm GPz900R carburettors were modified to suit the needs of the engine and a sump, complete with oil cooler outlets, was fitted from a GPz750 to keep the life blood pumping freely and staying cool. A home built, but no less professional looking, wiring loom was next up, allowing the fitting of a Dyna Coils ignition, replacing the old contact breaker set up and improving the power of the spark immeasurably. Z900 forks and yokes were press ganged into holding the front end up, while a Z900 master cylinder carries out the required braking duties, pumping its fluid down to the two Kawasaki calipers now fitted with stainless steel pistons and new seals. These in turn grab a pair of heavily machined and drilled Kawasaki discs, the stopping power could never be in question. A pair of Z1000 clocks tops off the front end, these maintain the looks of the Z650 but are just far enough away from the idea of a restoration to keep Simon happy.
At the other end of the bike a pair of Ohlins shocks originally intended for service aboard a Z1000, these kick the rear end up by a good amount, making the bike look alert at a standstill and keeping the rider alert when moving. Both wheels have been rebuilt, once again by Simon, using stainless spokes and alloy rims keeping the period look as much as is possible. The lovingly applied paintwork and stove enamelling was carried out locally by KG Sprayers in Aldershot while all other work was carried out either by Simon or a band of close friends.
Finishing the job off is the stumpy four into one, Harris exhaust pipe that not only shines brightly, but also creates a throaty roar unique to this machine thanks to the unlikely engine configuration and set up. The system is clearly good for the power development too, working in conjunction with the perfectly set up, big bore carburettors to get this special engine breathing as few others could. Simon is laid back and modest about how and why the machine came about with no mention of the difficulties this sort of work always creates, to hear him talk of the Z650 special is as if it “Just happened”, however, he is clearly a talented mechanic as well as someone who enjoys a machine able to get just that little bit closer to the limit and stay there all day.
The result is a far more powerful feeling engine with a wide spread of power and bags of torque all wrapped up in a chassis able to take the knocks and still keep going as if nothing has really happened. It still looks every inch the Z650 that it started off as but with a few cleverly chosen and applied modifications. In the near future an oil pressure and level light need to be added just for the safety of the engines sake as when it is ridden then it is usually up in the upper end of its performance envelope and any failings in the lube area will quickly undo all of the hard work spent putting the big bore engine together.
What’s it like then?
On the road, Simons Zed feels lively and ready to go, on the day we tested the bike we had a bog standard 650B to hand as well so the differences were plain to see and feel. The bike steers faster mainly due to the jacked up rear end while the Z900 front forks, and lightened and drilled discs, make the front end feel as if on the safe side of flighty, but only just. In corners, when the standard machine is way past the point of losing its composure, more than likely dragging footrests and side stands along the tarmac, and has decided to do a little dance to hide its embarrassment, the special is still in complete control. The Ohlins twin shock set up, borrowed from a much heavier Z1000, is totally at home and makes light work of handling the duties at the rear end. Being around two inched longer the jacked up rear end gives a good deal more ground clearance while also serving to sharpen the head angle and speed up the steering. The wheelbase is shortened by this action too making the whole bike feel more alive and ready for action that a standard machine. The original Z650 is still in there that is apparent but it is like the whole job has been energised and charged with a real mission. Every aspect of this machine works well and has been built around the needs and desires of the builder and owner. He knew what he wanted as a practical, fun bike and, although he could not fully describe why or what he wanted, he needed only to point me in the direction of the sort of roads he uses it on for me to get the message. Simon lives in the middle of the South Downs and the roads that make up this area can be a real challenge for the average machine, especially if a sporty ride is the desired way to travel. Straights are few and far between, one tight corner is often followed by several more in quick succession, often with ever tightening apexes and all manner hidden challenges along the way. For a bike to take this lot on without highlighting its own deficiencies is a tall order, however, once in this environment, the special Zed did all that could have been asked of it, romping into around and out of the twist and turns that make up the part of Hampshire and West Sussex where it and its owner lives.
Simon has resisted the temptation to chase the ever-widening tyre syndrome, often the disease caught by special builders who think that gracing a 30 year old machine with modern wheels is the way to go, and because of this his machine has kept all of the old attributes and gained many new ones. It is light on its wheels, with a small contact area and the resultant lower tyre friction, making switching from one side to the other a real breeze. Helping in this respect is a pair of wide bars that just like an old US Superbike racer gives total control of the proceedings at the expense of a sit up and beg riding position. The only fault I could find while riding this machine was the extent to which the rear and front end have been jacked up, not that it adversely affected the general handling quite the opposite in fact but when hard on the brakes the bike does cause a bit of weight shift, no doubt due to the higher position of the engine within the overall centre of gravity and made worse with the rider higher still. The bike never loses it though, it just passes that bit more load through the forearms and on and out through the bars, without the standard machine on hand to compare it too I would say even this would have passed without complaint.
Simon’s aims to create a back lane hustler have been achieved and his machine is more than capable of hassling some far bigger machinery around the twists and turns of the South Downs. Overall there is little to fault with his machine, it steers well, stops superbly and goes like stink thanks to the flawless set up and increase in capacity. Kawasaki got a lot of things right with the original Z650 concept but Simon has grabbed the ball and run with it, what he has built is a machine that, with just a few tasteful and well thought out modifications, is greater than the sum of its parts, being faster, more agile and feeling a good deal more sure footed too. As an added bonus, Simon’s special has a factory built feel and finish, never easy with what is effectively a second-hand parts-bin special, this is no mean feat especially as the look and the character of the Z650 has not been lost in the mix. The really impressive thing is the way he has gone about the job too, with minimal outlay for the parts and by making do, he has chosen to use his mechanical talents to overcome the many obstacles he has undoubtedly encountered along the route to his perfect bike.
For me it’s the perfect special, it looks like a standard bike and yet has a real giant killer ability and attitude, able to sneak up on the plastic rocket brigade, dressed like power rangers on their multi thousand pound steeds, dive underneath the lot and make off into the distance with little more than the evocative sound of that Harris pipe and the distinct smell of a hot, and hard working, air-cooled four-stroke motor. Sunday afternoons will never be the same again.
Kawasaki “Z650” B1 special Specifications
- Engine Air-cooled four-stroke DOHC
- Capacity 739cc
- Bore & stroke 66 x 54mm
- Compression Ratio 9.5:1
- Carburetion 4 x Keihin CVK 34mm
- Max Power 77bhp @ 9500 rpm
- Torque 48ft-lb @ 6800 rpm
- Ignition Dyna coils electronic
- Transmission five-speed, wet clutch
- Frame steel tube twin cradle
- Suspension 36mm telescopic forks Ohlins twin shock rear
- Wheels 3.25 x 19 4.00 x 18
- Brakes 275mm disc, single-piston floating-caliper, 180mm single leading shoe drum
- Wheelbase 1410mm
- Weight 211kgs est
- Fuel capacity 16.8 litres
- Top speed 125mph est
Kawasaki Z650 B1 Special Gallery
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