The problem with motorcycle forums is that they can become very "cliquey" (I think we had a thread about that awhile ago) and we tend to value some members comments over others depending on how popular they are, as opposed to how much they actually know about the subject from first hand experience.
I've seen this on this forum many time when folks here talk crap about Harleys, even though they've never owned one much less ridden one, and on this thread of course when the old "bad handling" stories about Z1's come up regularly.
I've owned both, and ridden thousands of miles on each, and I can happily reassure folks here that there is little real truth that well maintained Z1's are the "Widow-Makers" that some folks would make them out to be.
They did have problems though, like our CB750's and just about every other large Japanese bike built in the 1970's, most of the R&D was done on the engine, and the chassis was only sorted out after years of evolution. (in the Z1's case, not until the 1980's, in GPZ "Ninja" form) They had insufficient frame bracing, pathetic rear shocks, spindly 35mm forks with minimal damping, and tyres that were just awful from day one.
My new Fugly CB750F that I bought new in 1978 (discontinued model) was just as bad, those OEM Bridgestone tyres were just plain dangerous, and I swapped 'em for Avon Roadrunners when the bike had only done 1000 miles.
I bought my 1975 Z900 in 1985 with only 4000 miles on it, it handled as well as my CB750K1 that I had at the same time, but had heaps more power and torque, and this tended to exacerbate it's handling issues. I used my tax refund that year to sort it's handling issues, and installed progressive springs, S&W air kit, steering damper, Marzocchi Strada rear shocks, and Pirelli Phantom tyres. This went a long way to sorting it's woes, as it would with most bikes of the era.
Kawasaki engineered an extra problem into the Kawasaki frame that our Honda's didn't have though, the steering geometry was all wrong. The fork rake was way too steep, which made for sharper steering, at the expense of stability in a straight line.
At speed the combination of steep geometry and the rider's upright seating position with the high "Cow Horn" handlebars made the front end feel very light and "twitchy" at high speed. A good steering damper would control the "tank slappers" that Z1's were known for, but equally, better tyres and shocks would prevent them from happening in the first place.
Most well maintained Z1's that survived the 1970's Chopper/Cafe Racer/Drag Racer era will handle acceptably with just a few hundred bucks spent on sensible mods, and are a joy to ride. Add that to the fact that they're one of the sexiest looking bikes ever built, and I couldn't think of any reason (apart from perhaps the fact that they are horribly overpriced for what they are) not to buy one.
The reason that I'm not in the market for another one is that I can buy 4 or 5 more modern bikes that have tons more power and better handling for the price of one Z1, and I'd rather have 4 or 5 different bikes than just one. Different strokes for different folks, I guess? Cheers, Terry.