thank you for explaining me this!
i dont know nothing about the advance curve: this distributor is the breakerless marelli plex fitted on the mid '80s fiat UNO\regata\ritmo 1.3, it has the vacuum system, but i left it unconnected (will try sooner or later to connect the hose to the induction manifold)
will retard the advance, fit a set of NGK BP6ES and test the car; to retard i have to turn the dizzy clockwise..correct?
i suspect more an ignition issue than a mixture problem: never changed carburetor setup and the car, before the dizzy swap havent had any problem (brown spark plugs, on the rich side rather than lean.)