Small Engines (Lawn Mowers, etc.): Toro riding lawnmower quits when it warms up, toro wheel horse, riding lawnmower

Question
Hello Marc,

I have a Toro "Wheel Horse 8-25" Model 70040 riding lawnmower that starts okay, but when it gets warmed up and been cutting about 4 or 5 minutes or so, it starts to crap out and eventually dies.  Adjusting the throttle when it starts to run rough has no effect.
I have fresh gas and stabiliser in it.
I tipped it up to change the blade and got massive smoke after but it cleared up okay.
The problem seemed to start just after this happened - a coincidence? The oil level is good and it seems to run okay cold.
The spark plug seemed okay but I have not changed it.

Thanks in advance for your help. Appreciate it

Chuck.

Answer
When you tip the engine in any other way but spark plug up, the engine oil can run into the cylinder via the PCV hose and/or valve guides....this is normal.  Your problem sounds a little more like either ignition failure due to heat or a problem with burnt valves.  If it's valves, you should be able to shut the engine off, remove the spark plug lead and crank the engine over.  You should hear a whisping noise through the exhaust is the valve is leaking.  If not, connect a timing light to the spark plug lead while the engine is running poorly and observe the strobe flashes.  If the engine is missing you will be able to see it in the light.  Hope this helps.