From experience.. always check ignitions at the 4000 rpm recommendation.
Lower Rpm settings will sometimes run rough. Be sure to get the engine to operating temps..
Also, do not be fooled by thinking carbs will not mask themselves as ignition.
Be sure to do a manual sync... Then a pneumatic sync. Be sure the choke is returning.. sometimes the choke cable will get caught.
Don't assume.. Check the obvious first.
Personally we have chased ignition issues only to learn we had needle clip position wrong ok no a carb rebuild.