Hi i have a scag mower with a kawasaki FH480V KAI motor its a v twin 16 horse with 145 hours on it. The motot will randomly rev high and low, sometimes it runs fine and sometimes it will start changing rpm levels. Its almost as if when a mower runs out of gas it wil start reving up and down and almost want to stall out. I changed both plugs, fuel filter, oil filter and oil last week and it still has done it since. what could be causing this? with only 145 hours on the motor i wouldnt think i should be having issues yet thanks for the help in advance!!