OK, we have a liquid cooled 27 HP Kawasaki engine model number FD750D-S04. It has a very bad surging problem from half throttle and above as long as it is not under a load. Once the blades are engaged or if you drive up a hill it smooths out and runs great. Another thing is it backfires and sputters when we take it from full throttle back to idle after it has been ran for a few minutes. Is there anything we should look at to try to sure these problems? The only things we have done so far are new fuel and air filters. Could it be an improperly adjusted governer? I really had no clue where to start.