Once the mower is started, the engine runs fine, until the clutch/brack pedal is released, then the engine quits. Where would be the first place to check for a problem? Grateful for any answers!:)Thanks!

Hi,
Does it sound as if it labors and dies? That is something binding the drivetrain. Does it just die like it is cut off? That would be the seat switch(operator presence) "saying" that it does not know anyone is on the seat.
Peace,
Clarke