My 12A out of a 83 is having starting problems. Once i get it running (which takes a while) it runs great, restarts EVERY time, but starting it initialy is a bitch

It will start.. run real rough..and die. If i hold it at about 3.5krpms it will start to pop.. then smooth out and i can slowly let it down to a nice stable 1100 or so RPM idle? once it is warm it runs fantastic. What gives here? is it time for a rebuild?

OH, it's on a modded nikki no emisions, header, exhaust.

Thanks,

Daniel