The B with the hole was on my 49 w/216 when I bought it. I put a kit in it and it ran ok. I finally ditched it for a carter YF, but I don't think the hole had anything to do with my carb problems(typical B, airhorn warped, running rich). I do remember asking someone about it when I did the kit. maybe call Carbking at his shop, he would know, and seems to be nice to talk to.
