I've run two Zenith 228s for a couple decades now. The ones I have came on GMCs but I don't know what size engine mine came off. They have adjustable main jets, which can be too much of a good thing. There is a temptation to lean it out "Just a little" in hopes of bumping the gas mileage. These main jets were optional to compensate for trucks running over a wide range of altitudes. Lean it out when you get to the Colorado Rockies or when you leave Ogden UT for a trip to Denver. But DON'T forget to turn the jet back out again when you get to the California desert. I did exactly that and burnt a piston.
All this said, I had a Carter YF at one time and the truck ran beautifully and got reasonable gas mileage for such a truck. After I put one of the two Zeniths I bought for a song on my pickup, I "lent" the YF to my GF when her 56 needed a carb but I never got it back before she sold the truck.
I had a YF on my 50 Stude Champion whose 170" flathead six delivered 28 MPG on the road consistently. While working on the YF, I substituted one of the Zeniths and both power and mileage dropped a lot but it ran smoothly. I surmise it was too big a carb for the little 170. I was glad to have the YF back in service when I finished overhauling it. It had an automatic choke that I liked and worked well. The Studie was a nice car, quality wise right up there with the top of the line GMs. I'd still have it but for rust I couldn't deal with.
