Small Engines (Lawn Mowers, etc.): Mower runs, but dies when I put it into gear., toro riding mower, fan shroud

Question
I have a Toro riding mower with a briggs and straton  engine. Toro Model number is 56175, and engines model number is 253707-0175-01. I changed the gas and put new battery in, and cleaned the spark plug. When I turn it on. It runs great for about ten minutes, and then putters really bad with bright flashes. Also when i'l try to put it into first or reverse, and it starts to move then dies. I hold the clutch and break down, but it still does it. Any ideas.

Answer
Is the engine over heating?  Have you removed the top engine housing, the fan shroud, and make sure the engine fins are not clogged with debris?

Have you been using the mower this summer or has is sat a while?  When was the last engine tune-up where the valves were checked?

Eric