I've got a pair of YF's on an Edelbrock manifold on my 50 216 and after a little tinkering they run great. No hesitation, fires right up with a little choke, even at about 20 degrees, and best of all don't leak like the Roch's. I'm very happy with them.
By the way, the rebuild kit at Carquest Auto Parts stores is their # 121A. It covers about all of the YF's from the looks of the instruction sheet and if I remember right was about $16.
