If you've been using it for awhile and it starts spitting or sort of popping (which is different from happy crackles), it's not wicking properly and on the way out. If you pull off the tip and look down into it, it will likely have a dark ring around the coil spreading outward.
When members talk about flooding, it's usually in reference to over-saturating the filler when priming the carto or during refilling. In that case, when you try to vape it there is too much juice to be vaporized and you're going to get a mouthful of juice and/or leaking out the bottom - both of which can be remedied. Spitting, on the other hand, isn't good. You can continue to use the carto for awhile if it's not driving you up the wall. Sometimes playing around with power level can squeeze out a little more life, but if you have a lot of liquid in the tank you run the risk of the remaining juice getting a weird taste.
My blog probably won't tell you anything you don't already know, but it has pictures of what a flooded carto looks like:
The Ocelot Method of Carto Filling (aka The Upside-Down Condom)
If you have juice in the tank and don't want to pour it out to put in a new carto, click on the link in my signature. It goes to a short video about how to do a "Hot Swap."