I have a 2019 Grasshopper mower with Kubota D902 engine that suddenly won't start at low throttle. I have always started it at the lowest throttle setting and it started just fine. Now, it simply won't start at the lowest throttle setting. I thought something was seriously wrong, and I was just about to start checking for air in the fuel system when I decided to bump up the throttle for some reason and then it started just fine. It runs just fine once started. Should I be replacing the fuel filter to see if that will help? The fuel filter has about 230 hours and five years on it. Other ideas?