[Bartholow]

I think you should usually call. Your kings are hidden, you're getting about 5-1 immediate odds. A jack will usually win you the pot immediately, a king puts you in a great spot, and it's unlikely to be raised behind you here (and if it is they both may have aces which is ok for you). If a raise could get it headsup AND maybe buy a free card it could be worth it, but usually in that kind of game if they call one bet they are calling again and you're just building a big pot, with yourself caught in between.

On 4th I'd usually call if it looked like it was going to be one bet, but be wary of being caught in the middle.

5th is where you'll need to really evaluate, but the safe play would be to get out if you haven't improved and the Ac keeps firing.