I didn't drain the gas from my tank at the end of the season last year. I have drained the tank now. I replaced the spark plugs. The carburetor was rebuilt towards the end of the season last year. Fuel filter is fine. Battery is fine. I am not good with terminology...but when I turn the key it will constantly try to turn over for as long as I hold the key, but it never starts. I figured it wasn't firing so I changed the spark plugs. Is there anything I need about the plugs? Do I have to spray anything in there before I put a new plug in? The oil is a little low and probably needs to be changed, but I didn't think that would prevent it from starting.

Any thoughts? I can post the model number if you really need it, but I figured this was kind of a problem that relates to all mowers. It is a Craftsman with a 25hp Briggs & Stratton engine though.