Is there a reason for the cylinder one carb not to have this "jet restrictor w.e thing?". But anywho let me know not to familiar with these carbs. 1978 kz650 might I mention the bike runs amazing regardless. Which leads me to believe it suppose to be that way but I figured I would ask!
It would appear to me that at some point in the past the enricher (choke) fuel tube has been replaced with a copper tube. Since this tube is only used when the choke lever is pulled up I do not think it will create any issues.
Adding to what gd4now said, the "jet restrictor" is an emulsion tube for metering fuel uptake for the starter circuit or choke. On the other side of the carburetor directly above them, you'll see the starter/choke mechanism for each carb. The starter circuit or choke is an enrichener for adding extra fuel which helps start the motorcycle when the engine is cold. starter in this case not to be confused with the electric starter motor. hee.