ok, i've done some research and i looks like the big brass one above in the picture is the main jet and i dont even need to take them jet holders out if i'm gonna use the carbs that have the updated float bowls on. all i need to do i change the jets (leaner jets) that are in the updated carbs and use my non-updated carb main jets that are stock and put them in my updated float bowl carbs. then all is done to the carbs and then shes all ready. anyone disagree with me? i'm only new at this and i could be wrong!