I recently purchased my 72fj40 and so far all I have done is straighten out other peoples messes on this thing. Anyway I have never had it running correctly. When I purchased it I knew the engine was sick, so I rebuilt it. Now that the rebuild is done I am still having some carburetor problems. The idle mixture screw does nothing. You can turn it in or out all the way and it runs the same. The carb has been rebuilt and jetted to the manual specs. Although the thing runs good it is still not quite right. I would like some opinions on what to do. I give up on the original carb (it is a 9/72 build date, and I believe a California vehicle). I don't know what is wrong with it, but I can't find anything. So here is the question. Should I track down another original carb, go with a Holley, or a Weber??? The engine has a "RV" cam ( a little more duration I am told) and a header and a GM HEI distributor. Other than that it is stock. Any suggestions are welcome. Got anything you would like to sell? let me know. ???