most likely the gas, the newer gas these days doesn't like to sit more than 3 months...... it starts smelling like turpintine and loses most of its combustability... you can get fuel stabilizer when your car is going to sit for an extended time and it will double the life of the gasoline.... i like to put it in and run it for a minute before i let her sit, because when the fuel goes bad it can eat through carb gaskets a lot easier......