I have a 16hp Kohler on my Walker. It is three seasons old. Less than 1200 hours. Earlier this year the engine would stall first thing in the morning when I flipped the blade switch. I could choke it and then the engine would keep going and the blades would go. Now, it still tries to die when the blades first are turned on, but it also starts to die as soon as you begin to move forward. Seems like it takes 5 or 10 minutes to "warm up" Is this a sign that the engine is on its way out? I have changed air filters and inline fuel filters but nothing helps. The weakness problem seems to be getting worse. It also feels that it just isn't running as strong or as fast as it used to. HELP!