Which mixer tube BE3 or BE4

Hi i have a t5 with malossi kit 24mm carb the scooter has all ways had a BE4 mixe tube i see on this site some people have same set up but with BE3 mixer . Am i right in saying the BE3 is richer than BE4 i have tryed a BE3 in my scooter and i cant realy tell the diffrence what would this change by putting in the BE3 my main jet is 122 thanks Gary