I have 1987 Mercury Classic Fifty 45 hp 4cyl on a 16 foot tracker. Bought the boat in 2008 and it ran fine (WOT at 5000) for the next two summers. At the end of summer 2009, part of the throttle linkage broke and I had it repaired by a long time marine mechanic. When I got the boat back from the mechanic, the boat would fine for around five mins then the rpms would shoot up or the boat would bog down. Also, the boat wouldn't idle at all. I seafoamed the engine and changed the spark plugs and the boat has been running and idling perfectly, but only running around 4700-4900 at WOT. Tonight, however, after running around the lake for about an hour, the motor suddenly took off and shot up to 5400 rpms for about a minute or two, then settled back down at 4700 rpms. There was a noticeable increase in speed and sound of the engine. Does anybody have any idea what may be causing this? At first I thought the boat might be overpropped, but now I think it may be a carb issue. Could it possibly be the high speed jets are clogged? Is it time for a carb rebuild?
