Small Engines (Lawn Mowers, etc.): Mower wont start, brake switch, spark plug

Question
Thanks...my husband checked for a spark, and there is no spark, so now what?  Thanks for your help!

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Followup To
Question -
Our mower was working fine until just recently.  It is a Murry Ultra 20" Rear Bagging Mower, model #12H802 type # 2375B1. It was purchased in 1998 and has never been serviced.
My husband says that when you pull the string to start it, it only makes the puttering sound (like when you don't pull it hard enough to actually start it)...like it wants to start, but can't get there.  It has fresh gas and he tried changing the spark plug, same problem.  Any ideas for him to try?
Answer -
From what you've described, it could be one of two things.  The flywheel key may be sheared or the carb needs attention.  But first, you should check for spark by removing the spark plug and allowing the threaded portion to touch the engine while cranking the engine over...there should be a strong spark.  If the spark is OK, you need to try starting the mower.  After a few tries, remove the spark plug and inspect if it is wet or dry.  If it's wet, I would suspect flywheel key.  If it's dry, I would suspect the choke isn't working properly or the carb is dirty.  Hope this helps.

Answer
Because it has no spark, you need to disconnect the blade brake switch and check again for spark.  If it now has spark, you will need to adjust the switch or replace it if the switch is bad.  If disconnecting the switch makes no difference, you will have to make sure the flywheel to armature gap is 0.010"  If not, adjust it to that setting and check again for spark.  If you still have none, the armature is defective and will need to be replaced.  Make sure you take the numbers from the engine in to the parts dealer if you need the armature.  Hope this helps.