there are many things that could cause your car to fall on it's face and then clear up. i agree with what everyone has said but i must add, check on these items as well.
-fuel pressure?
-needle and seat clean?
-check your float level
-are you running power valves and if so has your car ever back fired thru the carb (must change power valves every time that happens)
It almost sounds like your carb is loading up on you when you leave the line.