heres my issues. im working on my sons johndeer tractor. it came with his house and was told it quit running a year ago. i cleaned the carb and adjusted it. i got it to start. when i turn the high fuel screw clockwise or in it should start to starve for gas and die. but it causes fire to come out the exhaust pipe. yes the muffler is shot. any ideas. also how do i test the stater and regulator and regulator for the charging system also. i do have a meter.