Back when I was 16 years old and knew everything, I replaced the 2 barrel carburetor on my 47 Ford coupe with a 239 cubic inch flathead V8 with a carb for a 272 engine from a 55 Ford OHV V8. It was a bolt-on swap since the 3-bolt footprint of the carbs was identical. The difference was in the venturi size- - - -the 239 carb had a 15/16" venturi, and the 272 carb had a 1 1/16" venturi. The result was a disaster- - - -there was a nasty flat spot at about half throttle that simply wouldn't go away unless I eased into the gas pedal like I had an egg between my foot and the pedal. Opening the throttle up quickly would result in a total refusal to accelerate, and usually a series of bad lean backfires. Gas mileage dropped by about 3 MPG. A week of that was enough for me to go back to the right carburetor.
Jerry
