From the diagrams at partzilla for the 1980 KZ550-C1 LTD. 16009-1061 JET NEEDLE,#4D93.
As for carburetor parts, I don't think there's much available for the Teikei carbs (TK-22).
KZRider loudhvx has a bunch of 550 carburetor info on his motorcycle stuff page.
click!
His site indicates a similar jet needle number of #4D93-2, with the 2 indicating in what groove to clip the needle.
The carb page has info regarding parts availability, changing jet needles & a bunch of other stuff.
