Never bothered with cored wire for my mig I have to say, I use argoshield light gas and occasionally get splatter in the tip, just gently clean it out with a small screwdriver and I carry on.
You will get more splatter with using co2 only, less with an argon / co2 mix. Also, can be caused if you're wire speeds not set right or your gas flow's too high or you don't have the gun at the correct angle for your weld or holding it too far from the welding material?