I serviced my lawn boy push mower last november, added stabilized fuel, replaced the sparkplug, cleaned the air filter, put it into a shed for the winter, pulled it out last week and now it won't fire. I am new to engine repair and maintenance so I am stuck. I pulled the sparkplug out to make sure the gap was correct and it was, i pulled out the air filter to make sure no critter had gotten into it, and it was fine. How do I know if it is the fuel or the sparkplug? How do I check it is or is not sparking?