I installed new Z therapy carbs.

now when started, it now idles at 3500-4500 rpm

When idle screws are turned in either direction it doesn't vary rpm's.

Any suggestions?

Well, figured out you can't hook everything that the flat tops had. Unhooked vacuum throttle control linkage, and now it works. Sure drove us crazy for awhile. Z-therapy carbs are sure nice. I enjoy all the info that one can get from this site.

You are using the wide carb spacers for the roundtops, not the skinny ones from the flattops, right? Otherwise, your linkage will be too long and not let the carbs return all the way down to zero throttle.

I learned this the hard way when I swapped out my flattops!