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The W650The Kawasaki W650 (1999–2007) stands as a beautifully timeless naked motorcycle, masterfully blending the classic British style of the 1960s Triumph Bonneville with the
renowned reliability of Japanese engineering. Its very name pays homage to Kawasaki's own W-series twins from the 1960s and 1970s (W1, W2, and W3), while the bike
itself captured the spirit of retro charm without sacrificing modern usability.
What truly distinguishes the W650 is its on-road demeanor. Despite a solid kerb weight around 216kgs, the bike's geometry …..27° rake, 108 mm trail, and a 1,465 mm wheelbase,
delivers surprising lightness and sure-footedness. It inspires genuine confidence, whether carving twisty backroads, navigating town traffic, or savoring a leisurely Sunday ride.
The upright riding position is a masterclass in comfort: high, wide handlebars keep wrists relaxed, the generous, well-padded seat supports the rider's back hour after
hour, and the footpegs are positioned just right for natural posture. Miles melt away with minimal fatigue, making it an easy, engaging, and deeply relatable machine,
ideal for everyday use yet brimming with character that elevates every journey.
In essence, the W650 is a motorcycle that consistently puts a smile on your face the moment you swing a leg over it.
What's not to love? For the more enthusiastic rider, the primary drawback has always been its modest power output.
The parallel-twin engine delivers a gentle, "put-put" character rather than outright thrust with just 48hp. This becomes especially noticeable with a pillion on board or
when attempting brisk overtakes. The successor W800 (introduced in 2011 with EFI and a larger 773 cc displacement) offered slightly more low-end torque but didn't
dramatically transform the performance equation.
The Pursuit of More Power: Engine Swap ExplorationTuning the original engine or sourcing significant aftermarket performance parts proved challenging. The W650/W800 never achieved the massive sales volumes of rivals
like the Triumph Bonneville, so a dedicated high-performance parts ecosystem never fully materialized. The options for meaningful gains were limited.
Swapping in an entirely different engine presented its own hurdles. The real difficulty lay not in sourcing a more potent motor, but in mating it cleanly to the frame.
After evaluating options, my focus shifted to a 1970s-era frame paired with an 1980s air-cooled four-cylinder engine.
The winner: the tight, compact frame from the early Kz650 B1 (1976–1977 models), combined with the Gpz1100 A3 two-valve engine (1,089 cc, delivering around 100 plus
horsepower in period form). The ultimate incarnation of Kawasaki’s air cooled four.
This pairing promised the best of both worlds; the compact, agile and sure-footed geometry of the Kz650 frame with the muscular punch of the larger 1100 motor.
The Kz650 frame's steering geometry (27° rake, 106mm trail, 1,437mm wheelbase) aligned closely enough with the W650/W800's setup to offer comfort, practicality,
maintain the retro look, familiar handling traits, while offering a proven foundation for the engine swap. Fitment was feasible, allowing the project to prioritize styling
refinements over major chassis re-engineering.
- 004 Rake and Trail table.jpg (84.45 KiB) Viewed 128 times
Compare the stock W800's geometry to the Kz650's and that of the ZX1100 in the table above. Culminating in my custom hybrid (W1400): tighter proportions for quicker
steering response than the big, heavy and long ZX1100, but paired with the added grunt that transforms this hybrid into a spirited, grin-inducing retro bruiser.
This custom build preserves the soul of the W-series while addressing its key limitation;
delivering classic looks with genuine muscle.
The project got serious once I started spending money and purchased the donor parts: a classic Kz650 frame from 1978, paired with a late-model Gpz1100 air-cooled
inline-four engine (the big, torquey flagship motor from Kawasaki's early-1980s era).
Rather than chase the Gpz1100's original top-end-biased character, designed for blistering straight-line speed, I prioritized the lazy, arm-stretching midrange torque
that defines a true muscle bike.
The solution?
A substantial upgrade via a 1394cc big-bore kit.
This capacity jump (from the stock 1,089 cc) transforms the engine's power delivery: deeper low-to-mid rpm grunt for effortless roll-on acceleration, open road overtakes
without drama, and that satisfying shove in the seat that the original W650/W800 always lacked. Why settle for subtle when you can have character?
With the engine destined for serious reconditioning, I entrusted the work to Ray and Steve at Debben Performance in Ringwood, ….the Hampshire specialist in classic
Japanese performance rebuilds, restorations, and modifications. Known for their expertise with Kawasaki's older fours (including crank work, head flowing, and big-bore setups),
they handled the meticulous prep to ensure reliability under the increased displacement and stress.
Thus, the
W1400 was born: a conceptual name that fuses the W-series' timeless retro silhouette with the muscular heart of a bored-out Gpz1100, all wrapped in the agile,
compact and surefooted Kz650 chassis.
The build philosophy stayed true; keep the light, agile feel of the original W while banishing the "put-put" character. With the frame's compact geometry providing the
foundation, engine fitment became the critical path -requiring the removal of the old engine mounts and precise alignment of new custom mounts, so that the engine
fits snugly between the lower frame tubes.
From there, the focus could shift to the real magic: a sympathetic re-style that honors the W650's classic lines while subtly nodding to its newfound muscle.
Once the ginder came out, there was no turning back. I had to be sure this was the right thing to do.
The goal promised to be far more than a parts-bin special. I wanted a refined retro bruiser; with comfortable upright ergonomics for all-day rides, predictable handling
on twisty lanes, and a genuine shove that makes every throttle twist rewarding.
Once complete, the W1400 would deliver grins in spades: classic style, modern usability, and torque that finally matches the bike's soul.
Let’s get butchering!
z650/1400 bonneville hybrid.
