It could be lean...or too much timing at cruise. I lean towards too lean [ pardon the pun ] because of the large cam. It will want more timing. If the carb has a choke: engine idling, close choke blade until engine runs rough; back off a tiny bit & secure choke blade in this position for test drive.
No choke: raise fuel level about 1/8".
Test drive.
If fixed, engine could be on the main jets...or transfer slot, which .
Have you checked the transfer slot position on the carb, 0.040" or less showing? If more, carb needs bypass air. With more air, idle jet will probably need enlarging slightly, 0.002-3". You could try bigger pri jets first, but I think this is an idle cct problem.