I have a Yamaha 115F I believe is a 1996 on a 17ft Mako. This past weekend we ran about 10 nautical miles offshore between 3400-4000 rpm's. We slowed to idle, and started back up again to appx 3500 rpm's. We ran for several minutes and the engine surged to about 4400 rpm's. I backed it down to about 3500 rpm's, a few minutes later it did it again and continued to do this over a 4 mile period. The engine seemed to be picking up momentum on its own. We returned to protected waters, decreased our speed and to between 3000-3500 rpm's and had no other problems. The seas at the time were only 1-2 ft. We had a recent tune up, and service on lower unit. A new thermostat was put in. Last year we had a fuel water separater problem, nothing else. Anyone out there that may have some ideas as to what causes an engine to surge and help steer me in the right direction to get this thing fixed. Thanks
