Small Engines (Lawn Mowers, etc.): Craftsman 6.5 lawn mower w/mulcher, mulcher, lawn mower

Question
When you try to start the lawn mower, it acts like it wants to start, but doesn't.  We changed the spark plug, but still no luck.  I read something about setting the gap, but not sure what this means or how to do it.  Can you help out?

Answer
Most spark plugs come pregapped at .025 on an inch.

How old is the gas, less than 30 days old?
Most likely the problem is a dirty carburetor.  If you do a search you should find lots of topics on cleaning carburetors or search for "Starts but dies" or something similar.

Let me know if this helps.
Eric