Have a 550 (09) that was just tuned up before it went out in the bush on spring bear hunts. Was running fine and the started to misfire and surge badly. Got to the point where it would not even stay started had to haul it out of the bush. Have got it to the point where it will idle for various lengths of time and then shut down (re-starts easy). When in gear it will find a happy spot and run ok but give it any gas and it starts to surge again not as bad though. When idling it will rev real high and then come back down and either shut off or keep idling depending on its mood. Also when idling you can hear a hesitation where it just about stalls and then catches again. Any ideas? Thanks.