Craftsman riding mower stalls when blades engaged?

Clean/replace spark plug and air filter. If problem persists, open needle valve 1/8 of a turn for a slighlty richer mixture, Something else to check. Some riding mowers have a sensor switch that will not allow the blades to engage unless the clutch is depressed. The switch may be faulty. Not sure exactly where it is located, but since it is activated by the clutch pedal, I figure that is the place to start.