I have a 2001 grasshopper with a 52 inch deck and a 20 horse kohler air cooled motor. When the pto is engaged and the blades are turning sometimes it will backfire and shoot flames out of the exhaust. was wondering what is causing this. Also it burns oil and seems to be lacking in power. I am wondering if the burning of the oil has something to do with the backfire and if so what could possibly be wrong with it. Thanks for the help.