I have a Kohler SV600 in a Cub Cadet and the engine will run for 30-45 minutes then start to die. If I pull the choke closed, it will barely keep running. I have rebuilt the carburetor, replaced the plug, fuel pump and filter. It almost seems temperature related. Has anyone experienced this? Any thoughts or ideas? I notice that the clear fuel filter looks almost empty (even when it is running well)