New carb, ZStar accels with zero throttle

[HO14]

Hello,

I am certainly not very familiar with auto mechanics but I did determine that my son's ZStar wasn't starting due to a faulty carburetor. I purchased a new one; this one has a choke on the carb itself as opposed to the old one which had a lever that was engaged by the choke cabling.

Anyhow it starts right up but accelerates to very high speeds without any throttle. I dialed back the idling screw but this has not resolved the issue. Can't think of anything I've done incorrectly with the installation and am uncertain what to try next.

Any thoughts? Your comments/help is greatly appreciated.