1975 z1 high speed wobble

what can i do to fix this problem when i get to higher speeds?

Speed wobbles can be very time consuming to track down. I would start with:

1. Are swing arm bushings worn to the point of replacement.
2. Correct tire pressure has a lot to do with this.
3. "cupping" of the front tire(looks like someone removed a teaspoon of rubber from the front tire)
4. Excessive wear in the steering head bearings.
5. Has the bike been dropped and is the frame straight?
6. Does the bike want to track anyway but straight when the bars are released for a short time?
7. Are the rear shocks worn out and have you replaced them before?

These are a few things to look at.

Plus:
Fork oil
Fork springs
Fork seals
New forks
Kidding of course, but Z1's have always been pretty well known for their interesting handling. I'd say your major things to look at would be new tires (if they're worn) + pressure, swing arm bushings, and steering bearings (I would suggest tapered roller bearings if you're going to be replacing them anyway)

Running Kenda tires will do it also. Mine looked loke a tire but did not act like it. I switched to dunlops.

The first after market accessory I bought for my new Z1 35 years ago was a Kawsaki OEM steering damper that fit perfectly on the brackets already on the bike from the factory. I guess it does the job because I have never had a problem with high speed wobbles.