I just bought a used X2503 60" with a 25 hp kohler and every thing is working great except for a loss of engine power when mowing over leaves? I mowed some tall grass and it did ok without bogging down but when I mowed over sand and leaves the engine feels like it wants to shut down. Any suggestions on what the problem could be? I would think this size engine could handle the leaves without bogging down. Any help is greatly appriciated.