Small Engines (Lawn Mowers, etc.): lawn mower, s yard, valve job

Question
Last week I was mowing my mother-in-law's yard and the mower was running fine.  I turned it off for a short time to do something else and when I tried starting it again, it wouldn't start.  I replaced the spark plug but it still would not start.  Any ideas?

Answer
You need to see if it will start now (when it's cold).  If it is a problem related to heat and/or time, you need to check a couple of things if you get it running again.  Typical heat/time issues are ignition problems or compression problem related to burnt valves and/or not enough valve tappet clearance.  If you get it running again, use it until it's good and warm, then shut it off and let it sit for a minute.  Check for spark (should jump 1/8" gap).  If no spark, you will need to replace the points and condensor (if old enough mower) or the ignition module if newer.  If you have spark, you need to listen to the engine as you slowly rotate it over.  Remove the plug lead and keep it away from the spark plug.  Slowly rotate the engine and listen for a "whisping sound".  This indicates compression leaking past the valve(s).  If this is the case, a valve job will need to be done.  Hope this helps.