Why does my lawnmower die when I engage the blades?

Definitely check wiring and all switches, starting from the ignition switch, behind the panel.

Occasionally over the past year my John Deere Sabre would be difficult to start, and more recently every time I would fully engage the PTO lever for the mower deck, the engine would die.

$500 in parts and labor later (carb, plugs, fuel pump, fuel filter, battery) I discovered that the wiring harness/plug behind the key on/off switch was loose.

When bumped slightly by the PTO lever engaged, it would loosen and engine would not restart until the loose switch/plug settled back into place temporarily.

Another sign that it was loose wiring or a switch should have been that sometimes the engine would die while rattling around over a bump, even without the PTO lever engaged.

Try disassembling the top part of the motor, then heavily spray the vertical shaft with WD40 or something equal, to dislodge any minute debris that may be on the shaft that turns your blades. run the engine for 5 min or so. Then after, engage the blades very slowly to try and prevent shut down. Hope this helps.

As another solution, I would also be checking the safety cut-off switches under the seat or on the drive, Or, could be a simple wire come off from the electric clutch that controls the blades.