Small Engines (Lawn Mowers, etc.): lawn mower wont rev up, tank fuel, fuel line

Question
My several-year old Craftsman 4 stroke lawn mower will start and idle nicely, but just won't rev up.  The cables appear to be moving the carb throttle just fine, but the engine speed doesn't advance above idle.  I cleaned the tank / fuel line / carb bowl and everything is clean looking, as is the air filter.  This is running on fresh gas.  The spark plug is pretty dark, but spark appears pretty strong.  Thoughts please?

Answer
What is the Craftman model number?  You will find the model number on a sticker, about the size of a business card.  The model number format will be something similar to xxx.xxxxxx or xxx-xxxxxxx.

I need the model number to look up your mower's information.

Eric