Back in high school (when we had genuine gasoline), the commonly used main jet in the 235 Rochester was either 56, 57 or 58. 56 was lean, 57 was normal and 58 was richer. We all mostly used 57 because we were at 5000 feet elevation. Today if you're using ethanol-laced gas, a jet one size richer will help compensate for the change ethanol provides...ethanol will actually generally burn leaner. The main thing is to figure out what mixed breed of parts are in your Rochester and then figure out if they're warped (and how much) and by the way...you have to also make sure the inner part of the carburetor isn't warped also.
Some folks will preach "use 2 gaskets" for a fix when the castings get all warped. The attached image is one reason why I don't like to see that done. This duo of gaskets was removed from one of the Rochester B models. If you look very closely you can see the person trimmed one gasket for the main jet mast and you can see the interior part of one of them was sucked into the carburetor's bore and that turned it into a vacuum-leaking and gas sloshing mess. Every time the vehicle went around a corner and the gas ran up in the float bowl, it would pour right into the throat of the carburetor.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
