83 kz550 now starts but idles way too high.

Wouldn't an extremely lean mix cause high RPM too? I seem to remember this happening on a bike when the fuel was turned off before it died.

I know I'm a bit late to the party, but here's a tip I found after I rebuilt the carbs on my '82 550:

Check your exhaust pipes.

On my initial start up, I found the bike at first idling seriously high, like 5000 rpm. I noticed the slightest bit of exhaust coming from the #3 header, the bolts were slightly loose. I likely didn't notice it before because of how poorly the bike had been running.
I torqued all the bolts on all 4 pipes down and on the second start, voila! 1800 rpm idle. A little adjustment and now it runs smoothly at 1100 idle.

I hope that helps!