Just bought 1986 Tracker V16 w/25HP 1991 Evinrude. Electric start fired up right away and it ran very well (22mph) when I first tested it out last week. Actually used it for the first time yesterday to fish and it ran well from one end of the lake to the other with no issues. I used the trolling motor for a bit and then decided to head back to the dock. Fired up, no problem. Then it started surging (I think that's the best way to describe the problem). Every 2 or 3 seconds it would lose power and then rev back up. Any thoughts?