Small Engines (Lawn Mowers, etc.): mower not starting after sitting for a month, engine model type, john deere mower

Question
QUESTION: when my john deere mower sits for more than a month it will not start. It turns over and there is spark.  If I remove the gas cap and blow in the gas tank to create some back pressure, then try again.. it will start.  My questions is....how do I fix this problem, without having to blow in the gas tank?

ANSWER: How old is the mower?  What model do you have?  When the mower sits is the fuel tank full or empty?
Let me know.
Eric

---------- FOLLOW-UP ----------

QUESTION: Hi Eric,
Thank you for responding so quickly.  The mower is 9 years old and the fuel tank is usually full or at least half full of gas at all times. I'm not sure on the model of the mower.  I will have to get back to you.

Answer
When you blow into the tank you are pushing fuel into the carb.  I have found defective gas gaps that can cause your problem but bad gaps are rare.

Let me know what model mower you have along with the engine model, type and code numbers.  The mower model will be found on a sticker on the mower frame.  The engine numbers will be found on the engine either on a sticker or stamped in the valve cover or engine metal shroud.

Eric