My personal experiences and impressions regarding the Z1 and Z1000.

For decades, the Z1-900 was the only bike for me; especially during my first 20 years of riding, it simply had to be a '73 model...!!! Than i have had `74 and `75 models for years also.

And i rode my last Z1-B  from `97 -`17 for 20 years and well over 100,000 km (rebuilding the engine twice during that time—boring it out to 1015cc on the last occasion).
Alongside that, I also rode two modified Z1000s starting in 2005...( My MadMax-bikes), though I had been wrenching on them for much longer...

Make no mistake: the Z1/Z1-B is the far more beautiful motorcycle—starting with the slimmer tank, the lovely side covers and tail section, the oval taillight, and so on.
From a technical standpoint, it offers better and "snappier" acceleration thanks to the lighter crankshaft...! And of course: I ever like the VM28 carbs!!!!!

But all in all, the Z1000 A1/A2 is the better bike for me:
For example: Stronger frame tubing, a thicker-walled engine casing, steel valve guides instead of bronze, a needle-bearing swingarm...
All these factors combine to form my verdict regarding durability and roadworthiness over the long haul with heavy use...!

But there is no question: The Z1 series bikes are the much better-looking, prettier machines - I still really love them immense!!!(I’m getting on in years now... I own two Z1000s and am very happy with them!
... but in my "dream world," a '75 Z1-B in its original "red-black-gold" paint scheme would be sitting right here!!!! - I’m always happy whenever I spot one somewhere...!   Long live the Z1-models!!!)       

Kawasaki created a legend when they made these bikes!