Small Engines (Lawn Mowers, etc.): Craftsman gas trimmer, air gap, gas trimmer

Question
I'm having trouble starting my Craftsman gas trimmer model 358795543, some 3yrs old with about 12hrs running time.  I first changed the spark plug, then put in some fresh gas and still nothing.  I've read in your past responses that the coil/ignition module could be the problem.  Could you tell me roughly the price for this item and could you further explain the air gap of .020in.?  How do you go about measuring this so that the coil seats in properly?


Answer
You can go to searspartsdirect and it will give you the competitive
price of the part.
 The clearance is not that critical, a business card works just
fine.

   Remove the air filter, and squirt some fuel or carb spray into the carb and try to start, if it fires up then dies, then you have
a fuel problem.

Checking for spark is a little tricky, as the trimmer has a lot of plastic, plug the coil wire on a new plug, and lay the side of the
plug against the metal of the block and pull the rope, if you have
to use a screwdriver to touch the block and the plug to touch the
screwdriver, that will work, test for spark.

Let me know what you find.