After I installed new mower blades, I "took a test lap" and everything seemed Ok. Cleaned up my mess, got back on the mower, & it wouldn't start. Gas was really low so I added some. Have not been able to get it started. Siphoned gas out to get dirt out of the tank, blew air thru from the hose before the fuel filter into the tank, and refilled with gas. Still nothing. Am I down to replacing the fuel pump or did I miss something?