The key to tuning that carb is to have a good needle & seat. And to have a restrictor jet in the return line with a .040 hole drilled in it. Keep the restrictor as close to the exit on the carb as possible.
The next is to start tuning on the bottom & work your way up. There are 3 adj screws. The pilot & Idle adj are needed to be set first. then Low & Highs.................. I havn't tuned an old Round in a while, but if you take your time, you should be ok.
ski ya, Paul