Hi, iv'e had this engine for 1 year.Two mechanics have looked at it and they've rebuilt the fuel pump, changed gas lines, fuel filters but i still have the same problem.The engine will be running between 3500 rpm's and 5000 rpm's then it will drop rpm's automatically and then resume normal rpm's.This will happen once or twice every trip.Please give me an idea on what the problem may be.Thank you for your suggestions
Make sure there isn't air in the fuel lines. Its possible it could be a stator or firing problem. Ensure there isn't arc from plug fires cross firing (cowl off in the late evening or night). Check your coil packs under load. They could be breaking down once warm.