4 years old sears tractor - runs OK when blade is engaged, but sputters and dies whewn blade is disengaged ? I replaced fuel filter and line but it still does it = is this is fuel solenoid problem or is this a carberator problem or something more simple ?

Hi,
Sounds like a machine that has a permanent positive connection to the solenoid and is opening the ground to control the operation. This is done on a few Craftsman machines and generally indicates a bad PTO(blade) switch with the description of your troubles.
Peace,
Clarke