I would suggest that the fuel screw needs to be carefully removed and port cleaned. Use some kroil, wd40 or whatever you have to help unstick it.
Check that it appears to be screwed in straight with no signs of adhesive.
Use a good fitting screwdriver and work it back and forth to gentle loosen it up.
Once unstuck and new oring installed the adjusted for smooth running.
Was the plug just black or was it black and sooty?
You are turning the choke off after you have started the bike?