Many of the YF carburetors used an .081 orifice. Information I have on the 3211s shows use of a .076 orifice. Anyway, some of the cheap rebuilding kits you get may have a .091, .098 or .101 orifice. If you do a little geometry...we'll choose the .098 orifice for this...the fuel flowing through that orifice is nearly 50% greater than the .081 orifice. That is a significant difference. Your float and the design of the YF are wrong for this much flow...won't keep up nicely. If you're also using a one-piece needle in conjunction, you'll probably flood at idle, almost certainly will run too rich and your fuel economy will go down pretty much at all speeds (with the possible but arguable exception of wide open throttle). You need the spring-loaded steel needle and a smaller orifice. Other factors go into this...fuel pump pressure/volume, fuel line, etc but some of those flirt in my opinion a bit with minutiae and overall mean less than the size of the orifice. Jon (Carbking) may weigh in on this. He's posted lots of info about this topic over the years. Back when I did the study on the Rochester B, BC, etc in the 5 or 6 carburetors I used for the work I found 3 different sizes of orifice. You can see them below. I have no earthly idea what Rochester was thinking with these...the carburetors were all designed for use on the 235. Rochester never (to my knowledge) published orifice sizes but Carter did and was serious about it. Good luck!
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
