Unless the engine is racing/surging/ hanging  at Idle it's likely too rich Keihin's are EXTREMLY sensitive to Pilot settings. IF your doing all the jetting on a Tired engine your Pissin in the
 wind, It dosent draw on the carb correctly or move the correct amount of Air. I suggest you rebuild it and start where your at now. Also a incorrectly set up head Will cause you fits dialing in jetting especially at low rpms.