Kawasaki Z650 Custom by Darren Carter

Kawasaki Z650 KZ650 Streetfighter

Today we’re excited to bring you another build from our favorite Englishman, Darren Carter, the man behind the BSA Thunderbolt Hill Climber that drew so much positive attention.  The Z650, marketing in the US and Canada as the KZ650, was known as the “Son of the Z1.”  It was produced from 1976 to 1983, a bike intend to combine the agility of a 500 with the power of a 750.  Weight was 465 pounds (dry), and the inline four produced 64 (claimed) horsepower.

Hoover from BloodrunnersThe Z/KZ650 has become a popular platform for custom builds, including this KZ650 brat tracker we love, but we haven’t seen anything quite like Darren’s build before now.  We love the blend of old and new:  the original paint paired with ultra-slick swing-arm and underseat exhaust, and those high double four-inch headlights have us thinking of Hoover from Bloodrunners, the comic that helped start the streetfighter genre.  That said, our man Darren eschews such label-placing.  To him, this is simply a Z650 Custom.

Kawasaki Z650 Build:  A Cautionary Tale of Not Planning a Custom Build!


This is a tale of a good idea that became a bit of saga in the long ago days before “ e-bay”, when mates, breakers and classified adds were the main parts sources.

I first bought the bike, my second z650 in about 1988.  (The first, to my eternal shame, got chopped into a stretched drag style low rider and then shortened back to the late eighties style peanut tank bobber and was sold as an unfinished project.) This, the second, arrived as a “normal” modded z650.  You know: gloss black, cast wheels, 2-4 seat, 4 into 1 etc.

I then sold it–can’t remember why–to a mate, only to buy it back some months later, as he hadn’t got a licence and wasn’t planning to get one!  I rode it happily, commuting, trips to family in the midlands, days out, etc, for about 5 years, until a house move spent all my money and the bike was put to bed at the back of the shed.  I was determined to keep it until things became more “comfortable.”  I have seen too many people sell bikes at the first hint of a problem or to deal with a problem, only to deeply regret it when said problem has been dealt with or gone away.

During this dormant period, and I remember the day quite clearly as the bike wouldn’t start when I wanted it to, is when the changes started…and because I hadn’t really planned a custom bike to the extent it has turned out to be, one thing just led to another!

The plan was to fit a mono-shock swing-arm to update the looks and improve the handling, and after a bit of research and phoning around a GPZ600 arm was found in Bridgewater, Somerset.  It was couriered overnight “because I had to get on!” (Though I still wasn’t riding on the damn thing for another 15 years!)

This arm was chosen because it goes straight into the frame with just a couple of washers to space it and is roughly the same length as the original for chain fitment.  The twin tube metalwork for the top shock mount however got in the way of the standard airbox, so K&N filters now have to be used. One drawback of this swingarm is that it is designed for a 16” rear wheel, so chain adjustment is compromised when using a larger wheel, and I have to start halfway along the adjustment with a new chain so the tyre doesn’t rub the front of the arm, but I just have to put up with that!


Originally I braced a standard Kawasaki arm and once the arm was fitted it became obvious that a 17” wheel was going to be biggest I could use.  Luckily I had a mate who was breaking a GS500 and the wheels were still available–not an obvious choice, but sensible tyre sizes (I use a 140/80 rear and 120/70 front) meant I could get the drive chain past with no drama.  Well, I say no drama, but the GS500 uses a smaller chain than the Z650, so I had to do a bit of thinking on the sprocket choice to get the 530 chain to work.  A quick spin with a lathe saw a spare CBR600 sprocket fitted, lucky that the bolt centres were the same pitch.  The bike always felt under-geared, though so memore recent research found that an FT 500 sprocket would fit the hub with a bit of machining and raise the gearing by 3 teeth.

The front however was a different story!  I could have made adapters for the Suzuki spindle to fit the Z650 forks, but the disc offset and rim width were always going to be more trouble than I could modify out…mmm….so it became apparent that a revised outlook was on the cards, which meant new yokes required!  As I was on a budget of as close to “nil” as I could manage, the yokes were made from solid 20mm steel scavenged from the scrap bin of the big engineering firm next door.  The top one was bent and shaped to match the height offset and the looks of the original, the bottom one kept to a simple slab design.  I then machined pockets underneath to reduce some weight where possible and made and welded on the risers.  At this point, I found a set of Suzuki forks in a breakers to make the spindle situation a little easier.  These turned out to be from an RG500 and had anti dive, a nice period bonus! But they were a little bent…and needed top caps…and springs…more work to do!

I managed to straighten the fork legs perfectly using a small fly press and blocks of wood, and the top screw caps were made by a mate of the time, as screw cutting is a little beyond my machining ability, and I stumbled on unwanted fork springs for an fz600 by cross referencing part numbers in an old Mand P catalogue…happy days!

And so it continues…in my local breakers, I found some old Suzuki GSX1100 EFE front calipers in need of refurb and a steel front mudguard and then managed to do a deal on some wavey stealth discs (the only new parts I managed to buy)!  Stainless adapter plates were made to mount the calipers to suit the forks, and the larger diameter discs and a one-off billet aluminum fork brace to mount into a new pocket cut and welded into the mudguard with hidden fixings was made.  And this was then all fitted into the new wider yokes…and I was away, a rolling bike again!  I found a rear underslung GSX-R caliper in the free ads of my local town to complete the wheel set and so just had to make the stainless hanger/bracket /wheel spacer to mount it on.  I was starting to like the “look.”  Now I know a mono-shock and 3 spokes is a well trodden path for older bikes, but it just works, doesn’t it?


This is when the old black chrome Harris 4-into-1 started to look a bit understated.  This was back in the mid 90’s when Ducati started messing about with underseat exhausts.  I had tried before with modding old pipes for underseat stuff but this time I decided I was ready to go from scratch…and in stainless of course!  A few measurements and angles were made, a jig built, and four matching manifolds were produced and polished.  Mmm…that went well, I thought, and so it continued.  I made the two end can silencers with internal reflector plates and tubes to baffle the exhaust note and positioned them by chopping the rear of the seat frame a bit and mounting the famous Kawasaki ducktail straight onto the underside of the seat to allow max clearance.  Then it was just a case of joining the manifolds to the cans as nicely as possible.  I did this using the time-consuming cut and shut “lobster-back” method of tube forming, but it meant I could change direction and angle by tiny increments to get the lines as good as I could, the welding took ages and the polishing even longer but I am quite pleased with the end result and the exhaust note that comes out is just right!

Kawasaki Z650 Underseat Exhaust

The rear set foot rests and controls are all stainless with bronze oil-lite bushes and are fitted just behind the swing-arm pivot.  The kick start is now removed and I use a higher capacity battery just in case!  Some may feel the foot rests are a bit high, but after five mins riding, they feel just right!  However, as old age advances, their position may change.


The front lights were a bit of a dilemma.  They had to be twin, because that was rare at the time, unless you read Performance Bike, in which case we all had them!  They needed to be not too big and preferably cheap (or free).  One day I was out on a job and passing a waste skip (pattern emerging here?!), and I had a look in, as you do, and there they were:  two spotlights from an industrial powercut back-up lighting pack, 4” and working!  What a result!  These were painted to match the main body work and mounted on custom made teardrop style alloy billet mounts with hidden fixings and hidden security bolts for the lights.

The paintwork I can take no credit for, though I did a quick clear lacquer overcoat last year to gloss it up a bit.  It came with a former Z650 (the first unlucky example as mentioned at the start) that I had since parted with but kept the paint as it is so striking, in spite of it being nearly 30 years old to my knowledge!

So with all the engineering done and working, then came the traditional strip down and powder coat of all steel parts and the alloy wheels.  I made an engine mounting frame and painted the engine in high temperature gloss and polished all the outer engine cases.  (The engine seemed ok previously, so I thought there was no point stripping it at this point–that could have just invited more expense.)

This was followed by the final assembly and things were looking good, but then came the wiring, which when compared to the new shiney bike looked rather shabby and dangerous.  Nothing else for it:  out with the Haynes book, find out what does what and what colour it is, cup of tea, and make a start.  Well I say make a start–think and worry about it for a week and then make a start!  A long time later (weeks of dinner-time working), and a new loom was complete.  Not perefect but functional, including a clever little modification involving a relay in the ignition circuit that I picked up from an Australian performance website.  It links the ignition coils directly to the battery when made live.


There have been a few teething problems since the bike has gone together, carbs flooding and coils failing, hence the interesting exhaust manifold colours….but it was finished at last….that is until I saw a Metmachex swingarm on ebay and thought, now that would finish it off properly.  I was determined to get the arm and fortunately won it at what I considered a reasonable cost, and it was fitted with minimal fuss shortly after, and now it is finished!

As a first full project I have to say I am quite happy with how the bike has turned out, except with how long it has taken to complete!  With hindsight a few details could have been done differently, but they are not bad enough for me to remake–life is too short!

Yeah, this beast gets ridden.

The bike is a bit higher than standard and tilts slightly forwards so the fork angle is decreased to about 25 degrees.  But it rides just great, the balance is good, it tips into bends nicely and holds a line so much better than before.  The suspension is well matched front to rear and the tyres now testify to how well it goes round bends!  The only thing it needs now is a GSX-R750 motor, as it handles much better than it “goes” in my opinion!  This won’t be happening, though, as it is currently insured on a classic policy, and I am just happy they don’t cause trouble about the changes that have already been made!

It gets a nice bit of attention wherever it goes, which to be fair, though an unintentional bonus, I really enjoy, with conversations normally starting with:  “Nice bike mate…I used to have one of those when I was a kid!…wasn’t like that though!”

All in all, this has taken about 15 years to get to this stage due to budget and time restrictions but mainly because I didn’t start with a plan…and without a plan I didn’t know when it was finished!

Lesson learned?  Of course!  The next bike took only two and half years!  The transformation of a perfectly normal BSA Thunderbolt into a quick handling hill climber, but that’s another story…as you already know.




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  2. Brandon in RVA

    The fact that you haven’t seen anything like this bike before and label it a Brat Tracker means you haven’t been following custom bikes for very long. I’m pretty sure Streetfighter magazine featured Bloodrunners before it was any more than a one page comic. I haven’t picked up a Streetfighter in years, mainly due to the fact that everything started looking like it was built in Florida by a failed MMA punching bag. But if you look at the roots of that magazine, in the 90s, you will see a lot of bikes built like this.

    • Thanks for the feedback, Brandon. But you might want to read a bit closer. We didn’t call it a “brat tracker.” We said: “The Z/KZ650 has become a popular platform for custom builds, including this KZ650 brat tracker [link] we love, but we haven’t seen anything quite like Darren’s build before now.” That says nothing about Darren’s build being a brat tracker…at all.

      I was a member of the Custom Fighters forum more than a decade ago, so I know a little about streetfighters, but I’m no expert. It’s just been a long time since I’ve seen a build like Darren’s, and I’m glad to see something like this as opposed to the warped, insectoid, chrome-framed, fat-tired streetfighters that started coming out — the ones that you so aptly described as “looking like it was built in Florida by a failed MMA punching bag.” I’m dying. Dead-on, man.



  4. This is a mesage for Darren, I think I may have his earlier Z650 stretched/shortened bike and would be interested to know if this is it?

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