carb rebuilding and the sort

ok this is gonna sound crazy but i am missing the spring that hold the secodary flap shut on my 2.3 carb, so it is open at all time now i know it only squirts gas when i'm at open throttle but how bad it this extra air coming in for my per formance and mileage ?

i am talking about the flap on the bottom of the carb not on the underside if any one has any input please let me know

would a general rebuild kit have this little spring ( i know nothing about carbs and rebuilding them )

thanks