I have a Cub Cadet RZT L zero turn mower that doesn't want to crank without adding gas to the breather after sitting. Once I add just a spits worth of gas it fires and runs no problem. I can then kill and crank as many times as I need. Never have problems after the initial crank. It seems to be it's losing prime after sitting a few days and will not crank without help. It only has 15 hours on it and I've always used conventional gas since I bought it. Looking over the fuel lines and they look to be good no cracks or leaks still look new because I park in my shop. Can this be the fuel pump or fuel filter? Any help or advice would be greatly appreciated.