Ok, I hate typing essays. Let me lay a small footing......
Large cams - meaning more duration/lift will bleed off cylinder pressure. You went smaller cam, so that will raise your cylinder pressure.
A big question is "how much advancement was ground into the cam??" And when they reground, what about the advancement???? Advanced valve timing adds cylinder pressure.
So, between the two statements above, you gained cylinder pressure. This is effecting how the plugs burn. So you are now trying to compensate by Jetting your carbs, which will most likely lead you to "too rich, then too lean" conditions.
