Air bleeds, and venturi size are different, between the 340/440 carbs,....as are obviously numbers, venting etc,....and a few CFM differences between AT/MT 340/440's.......if you don't care about the "numbers" thing,.....340 end Carbs on a 440 will react faster to opening, regardless of spring tuning, vs the same spring tuned 440 end carb because of venturi/ orifice size