Hmm...never seen a YF1. Try Mustang Geezers website. He lists quit a few carburetors and their respective CFM ratings. However, you might want to say away from the 240 & 300 carburetors. You may have hood clearance issues. I think they are RBS'
Or...you could go with a Holley/Weber 32/36 like I did just last week.
It was cheap! 65.00 for the carb. and 15.00 for the adapter. Kick in about 3 bucks worth of aluminum stock and .... BAM!
It flows about 280 CFM and because of small primary, the low torque is pretty cool at take off.
-Chris