Oh yeah, if stopping the fuel flow results in the engine just idling awhile and shutting off suddenly, it's best to richen up the idle and test until you actually get the pinch test to show your setting is too rich. THEN lean that lowspeed back a click or two.

You know how everyone always advises that you run your highspeed needle a couple of clicks richer than the peak rpm setting on the ground? The idea is that the engine is going to run higher rpm in the air and is going to need more fuel when at flying speed. Same is true with the low speed needle/airbleed setting.