High speed wobble.

Experienced this myself on my 74 Z1900. I would guess there is nothing wrong with your bike. This is a well documented problem. Myself, it started at around 130. Keeping in mind that it took me a awhile to reach 130 from 120. Only after I laid on the tank behind the fairing did it start climbing again towards 130. My feet where on the back pegs. Once it started I backed off slowly and let it glide down without braking. It settled down again around 120 or so. I read years later in a cycle magazine that was given to me and was from the 70's. It had a write up on the new Z1900 and mentioned the high speed wobble. It attributed it to a weak head stem design which caused flex at high speed. I wish I could find that article.

Narower bars can help with this. It sounds like wind-steer to me.

My 78 Z1R front end would shake like a wet Dog at 120 mph. One time I tried to push through 120 and it just got worse, when I backed off it shook so bad it almost threw me off the bike.
I think its just the nature of the beast unless you gusset the frame.

Hey Duck,

Where you at in CO? I'm in Fort Collins and ride a '76 KZ900 Ltd. From my research the '76 frame was beefed up from the earlier models to help with this. I havent' had this problem, but I replaced all my wheel bearings 2 years ago during the rebuild. Also replaced the swing arm bushings with needle bearings. I had over a 1/4 inch play in the swingarm before I did that. Another culprit might be the neck bearings if they are original.

To be honest, I've been too chicken to go all out since the rebuild. Had it up to 125 on 34 east of Greeley and it was really smooth, but it felt like I was starting to lift off on the rollees so I backed down.

Let me know if you're interested in the kzride to carry the flag across CO. I'm not sure If I'm going to have to ride up to Montana or N. Dakota to get it, but once it starts moving again, I'm hoping to figure it out.

Good Luck!

Link

As Ed said, tires are at the top of the list, especially the rear. That's what cured it for me, and it's also mentioned in at least one constructor's book.

what about at 60? helmet cam?

Link:
I am just north of Boulder. I might be interested but I cannot guarantee if I will be free to do it. There is a good possibility that I have the time to do it though.

donthaveakawman wrote: what about at 60? helmet cam?

It is glass smooth all the way from 0 to around 115.
Above that, it looks like this:

On a scale of 1 to 10 what was the pucker factor?

I had a 9.9 pucker factor at 130 one time and it scared the heck out of me because it was so violent.

It will get your respect once you expierence it that is for sure

Try raising front end of bike back to stock level and snug up steering head bearings just to see if it helps

Pucker factor was fairly low to be honest. It was a strange feeling but it wasn't violent. It would have been bad if I tried to push through it because it got worse the faster I went.

I set the front end back up and I am going to change to 15w fork oil on Tuesday when I can get some more. I won't be able to say if it helps for a while as I rarely do speed runs like that. I am more into scraping foot pegs through the twisties however I don't like losing to a Ninja 500!

a steering damper wouldn't hurt but it is still an issue nonetheless.

wireman wrote: Try raising front end of bike back to stock level and snug up steering head bearings just to see if it helps

+1