I have a Walker 1999 with a 25 hp Kohler (1,600 hours, well maintained). When I first start the engine and raise the throttle, the engine runs on one cylinder. After a minute or two the 2nd cylinder ususally kicks in. Once the 2nd cylinder kicks in the motor runs great (normal power and rpm). It seems to do this any time it is turned off, even if the engine is warm. Does anyone have suggestion on how to diagnose?