Have a 25 hp kohler which has 1600 hrs. When it is warm and you idle it down and then give it full throttle it gives out black smoke and lugs down for 10 seconds to a minute. I have checked both coils and the SAM. The head gasket was replace a couple of hundred hours ago, but it seems like it acted kind of like this before the head gasket was changed. When it does reach full rpm it seems pretty strong. It does burn about 1 oz of oil per hour. Also, it you put it in a side hill it will cut out on me. Any suggestions are appreciated.