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.

If your lawnmower dies when you engage the blades, it’s often due to a safety switch issue, a clogged mower deck, or a problem with the engine under load. Common causes include:

• Faulty seat or blade engagement safety switch
• Worn or damaged belts or pulleys
• Clogged or overgrown grass under the deck causing excess strain
• Engine not getting enough fuel or air to handle the extra load

Check these areas for problems to identify the cause.

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Here's a variation you might not expect. On my brand new sit-on mower I had exactly this problem until I found out it only happend during first starts. Later I learned that from standing still the snares were sort of 'locked' in their form from standing still and the motor simply could not pull the first resistance at first starts. To overcome this, I started the blades while driving down hill at highest speed, to use the momentum of the mower to overcome this first resistance. Some years later this all disappeared as the whole mower was properly run in and snares had worn down a little bit. Of course you must make sure the height of the blades is still at maximum height while engaging, but I guess that's logic.