i have a low mileage 73 with what i guess are the original hitachi flat top carbs? they run fair, but was contemplating getting something newer and more reliable. Any thoughts/experiences on what to use?

This topic has been discussed many times. Do some searches for 'flattops' and other words like 'options', 'choices', 'conversion', etc. to see some of the previous talk.

Short answer -- for a mostly stock 240Z you probably can't do much better than a nice re-built set of round-tops. A set from Z-Therapy will work great out of the box, and will cost less than Webers, Holley conversions, etc.

A fix that was very popular when those cars were new was for the owners to bellyache to the dealers long enough and loud enough about how bad those carbs were in relation to the round tops from the earlier cars thus ending up with the earlier carbs.

Your flat tops were an interim fix prior to NISSAN going to FI.

We (Ztherapy) supply many sets of round tops to replace flat tops that are just now getting replaced, round top completes to replace degrading original FI systems, and of course, the replacement of run of the mill worn out Hitachis.

Others will be along with resource suggestions as well, but let me suggest a read-through of www.ztherapy.com for a good amount of information on those earlier round top carbs.

thank bruce, i will be in touch. i obvioulsy don't have the core's you need so i'm not certain if you have any or not.