It's all about the drop in flow per carb you get when going 2x 1bbl. It's not half, but the drop is still considerable.
You can tweak the 235 RochBs but they will never run as lean as the smaller 216 version.
I also started out with 2x 235 RochBs, then tried 2x 235 Carter YFs.
But no tricks or tweaking got the carbs to match the requirements of the 235 and make it run as well as it could.
2x 235 carbs are great for a 261 bored and cammed for racing...!
After confirming my experiences and talking to 'Carbking' I understood what was going on and now use 2x216 Carter W-1 and Stromberg bxov-2 carbs from 1948 on both my street 235 and 261.
Power, fuel economy and response from the throttle is ideal and I get around 20 mpg on the freeways.
I use 2x1 McGurk intakes, which always used 216 carbs, even for the 235 - the only 2x1 235 intake that got the carb size right for street use.
You can have a new repro Offenhauser 216 intake bored at the head ports for the 235 diameter.
That's what I did on my previous 235 setup.
Or you could also use the 216/235 adapter alignment rings from Buffalo Enterprise, which are the same cost as boring the intake ports.
That's what I use with the original cast 216 intake.
