I have a strange problem with my fuel flow on my new IO550 upgrade on my N model 35. If any of you have any ideas I would very much like to hear from you. After takeoff an into cruise flight, my fuel flow will momentarily surge. If I am running 2400 RPM and 23" MP and a FF of 15 g/h it will surge to around 18 to 20 g/h then settle back to 15 g/h. It does not do this all the time. I had a flight to PNS on Saturday at 8k ft with no surge at all. On the flight back home to SFB it surged three time, about 3 to four minutes apart. The surge only last about 2 to 3 seconds. If I run lean of peek the surge is not as pronounced but still there. I've had my mechanic look at it and he has made some adjustments to the maximum fuel flow settings but it still persists.