I have a Lazer Z with a Kohler CH740s. New plugs, air filter, oil filter, and blades. The engine cranks easily. Runs perfectly for 10 to 20 minutes. After cutting moderately thick grass the engine loses power. It sounds like its running at about 80% of full power. If you allow the engine to cool competely, the same symptoms can be repeated. On one occasion, I disengaged the blade, waited for about a minute, and could detect the engine return to full power. However, about a minute later it bogged again, and that was it for the day. The problem has been occurring for a while but appears to be getting worse. I have not checked the spark after this happens, so thats the next thing I plan to look into. Any ideas?