classic motorcycle forum

I am restoring a 67 Ducati 250 Dianna,now just sorting a few running bugs.The revs wont go over 4000,the ignition was magneto type,now battery/coil,I am told that the orriginal generator/mag is not suitable and needs a mod to fix, the bike is now 12 v, could the problem be overvolting?.Has anyone modified an advance /retard  unit as they are diferent for mag and battry bikes.I also need to check that the coil is right type for 12v, what ohms readings ?.Plug grade for todays crap petrol?.