Maybe I'm missing your point but maybe also you have it backwards. If the engine idles with the choke on, (closed, lever up) then you definitely have an air leak. If everything is sealed up well, choking the engine will stop it. In fact there are a number of guys who rely on the choke to kill their engines because they do use a kill switch. If I'm misunderstanding you, let me know but if your choke is closing properly but doesn't kill the engine start looking for a leak.
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