FWIW, many years ago I had a Studebaker Champion w/170 cu in L-head six. It came to me with a Carter YF, which developed a stumble off idle, perhaps associated with unleaded regular that was just introduced. While I worked on that carb, I installed a Zenith from a 228 GMC to keep driving it to work, etc. The stude ran OK but got terrible gas mileage by comparison with before. The Zenith had the adjustable main jet and leaning it out didn't help the gas mileage. I fixed the Carter reinstalled it and all was well and I was back to high 20s MPG on the road. During this saga, gas hit $0.50/gal so I was motivated to get it set to rights.

1951 3800 1-ton
"Earning its keep from the get-go"
In the DITY Gallery
1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.