The two most common mistakes people make is putting too much camshaft and too much carburetion on too small of an engine. Any piston engine is simply an air pump, and a carburetor works by converting air flow through the venturi into vacuum to draw the fuel from the float bowl into the air stream. Opening up a bigger hole for the air to flow through (or two of them) slows down the velocity of the air stream, and you get less, not more fuel from a bigger carburetor. If you're planning to run full throttle at high RPM all the time, a bigger carb MIGHT be a good choice.
The big bore 2 barrel Rochester used on the 307 is FAR too big to function well with a 235. It's more suitable for engines like the Chevy 350 or the Pontiac 389, and when it's used on a 305 Chevy or a 307 Olds, etc., the float level must be set very high to avoid a lean stumble. If you want to use a Rochester 2 barrel on a 235, find one of the small bore carbs that were used on the 265 Chevy V8, fabricate a modified intake manifold that allows the carb to be bolted on without an adapter, set the float level as high as possible without flooding the engine at idle, and learn to feather-foot the gas pedal at a stop sign. Have a good fire extinguisher handy in case of a backfire!
Jerry
