Kawasaki’s original 1972 Z1 was raw and uncompromising. And in the wrong hands, potentially lethal. When the subsequent Z1000J came out, the rough edges had been smoothed over—the styling was softer and the suspension was better sorted, even though the new model was lighter and slightly more powerful. Today, the Z1000J has attained cult status in Japan, and attracts the attention of top-flight tuners such as Sanctuary and Bull Dock. This particular machine comes from Bull Dock’s Sano City-based workshop; at first glance, the bike looks authentic, but the modifications are extensive. The DOHC inline four motor is now running a 10.25 compression ratio, rather than 8.9:1. It’s also been ported and polished—and more importantly, bored out almost 200cc to 1,197cc. Hotter cams and flat side Keihin FCR 35mm carburetors have replaced the standard Mikuni 34s. (So yes, power has probably increased a little from the stock 102 hp.) Fortunately, Bull Dock has upgraded the suspension too: the front fork is from a Zephyr 1100, and the rear shocks are Quantum items originally designed for the ZRX1100. You’ll stop faster, thanks to a braking system packed with GSX-R1100 components and four-pot Lockheed callipers. And keeping the rubber on the road are 17” Mitchell wheels front and back, shod with grippy Battlax BT010 tires. Impressed? Then check this Bull Dock gallery for more amazing custom Z-bike builds.