News flash.... you know when you check those little numbers on the carburetor boss... the ones stamped 32...34...36mm and on? Well, it might surprise you that most 36mm carburetors do not measure 36mm!! I found found differences as little as 1 mm between 38's and 36's. With this said, when a discussion over whether to use 36 or 38's comes up, I see very little jetting differences between the two. Also, the performance gains between the two are barely worth contemplating.