45 Carburetors

What model and year carb. do the 45's use? I came across some 55hp carbs and the venturi bore is much smaller than the two sets of 45's carbs that are on the two powerheads I do have now. I'm new to the sport and thought the 45sst used stock 45hp carbs. It's been my understanding the bigger the venturi the more air is received into the combustion chamber. Of course air velocity is another matter entirely. Anyway, if someone out there could tell me what it is all about I surely would appreciate any information. Thanks!:confused: