The first few minutes that an engine is running are generally the dirtiest. In the choked mode the engine is running over rich, and is not able to burn all of the fuel the carburator is delivering. Also, until the engine warms up the atomization is not complete, causing an over rich condition.
Age is factor, the carburator is forced my design to operate under the mechanical constraints of jets and other conditions all of which are governed by the carburators "tune" as well as the engines condition. Your wife's late model Cherokee has all of the operating ranges of the engine governed by a computer, that can make much more precise adjustments based on sensors.
