Speedometer acts very odd

Hi, I am new to the forum, and my speedometer on my 1979 kz 200 doesn't work. It will spin from 20 then go to 80 then sit at 0 and bounce all over the place. Anyone know what this is and how I can fix it?

I may just be a bad or poorly lubricated speedometer cable. I would remove the cable and slip the inner cable out of the sleeve and inspect it. If it appears damaged replace it; otherwise lube it well, re-install, and see if the problem persists. Ed