Small Engines (Lawn Mowers, etc.): Toro Tractor starts then stops, lawn tractor snow plow, tune ups

Question
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Followup To
Question -
We have a Toro combination Lawn Tractor Snow Plow.  When mowing, it starts up, then the engine dies and won't restart.  Much worse in the heat.  Toro dealer can't figure out the problem, it doesn't happen in the shop.  Any thoughts?  It is 6 years old and has been a problem the past two summers.
Answer -
What brand of engine do you have?
Have you tried replacing the spark plug with an NGK brand of spark plug?

Do you know what has been done to the mower so far?

Let me know.
Eric

The engine is a Kohler engine.  What are NGK spark plugs?  What has been done so far are regular tune ups, the needle in the carburator was changed last year and the gas was drained and new gas was replaced last year.  Also, last year a mouse was found to have built a nest in the flywheel.  The flywheel was removed, cleaned with air and put back on.  More description of the problem is that when I hear the engine start to stall, I shut off the blades to reduce the engine load.  It helps for a short time but then after about 15 minutes it starts to stall again.  If I shut off the blades again, the engine backfires many times then stops.  I can't restart the engine until it cools down.  Nothing like this happens in the winter when I use the snowblower attatchment.

Answer
You may have a defective coil.  Sometimes when the coil gets warm the wire coil insulation expands and causes a short.  I have never seen this but have read many articles about it.

NGK is a brand of spark plug...they are much more reliable than Champion.  We find many Champion brand of plugs that fail when the engine gets hot but then begin to work again when the engine cools.

Kohler valve breathers also seem to fail.  You can clean the valve breather or just replace it.  I would check all the tubes/hoses connected to the valve breather before replacing.

These problems can be the most difficult to troubleshoot and repair. Sometimes it's trial and error.  You may want to check E-bay and see if you can find an inexpensive used coil.
Let me know what you find.  
Eric