I have a 2000 or 2001 11 hoarse power Murray riding lawn mower. The mower will crank and idle as it should but when I release the break or engage the blades it seems to loose power and shut off. I have replaced the safety switch for the brake. The mower continues with this problem. Something I noticed was that instead of the mower not cranking when the seat is up and the safety switch under it is not decompressed it cranks regardless.

Typically if the switches make something happen then they are OK. What I mean is if you lower the deck and it shuts off then that switch is operating. Or if you push down the brake and it stops then that switch is probably Ok too. I would be more inclined to suspect the seat switch. If it stop immediately like you shut the key off then I would go to the seat switch.

But, what I am reading is that the mower slowly dies. If this is what you are saying then maybe you are not getting enough gas to keep it operating when you put a strain on the engine by makng it move or engaging the blade. If is slowly dies out try checking the gas cap to see if the vent hole in the center is clogged. If that doesn't help it sounds like you might need to clean the carburetor.