Just curious, does it want to die the same if you ease off the gas and if you snap it closed? If it behaves differently, is the carb supposed to have a dashpot to ease it down to idle (and is it adjustable?)?
I don't understand the cause but have met engines that wanted to die when snapped closed. Pulses in the intake? rapid change in mixture? Don't understand but would be glad to hear the technical why of it.
Except when needed to get the engine up to stable temperature and aid vaporization in a cold engine, it is normal to want cooler (and as a result denser, more oxygen per cubic foot) air to permit more power per cubic inch.
