Force Motor Running Rough at Times

[Oldsaltydog]

Here comes another novice question from a "ragbagger" turned "stinkpotter." My 1998 Force 90 idles smoothly, runs the same at low and WOT speeds, but it is fairly rough at "medium," pre-planing speeds. Is this a common thing or do I need to do something more to this fine motor? (The list of my completed repairs is long -- new battery, new plugs, carburetor cleaning and adjustment, fuel pump, fuel filter, water separator filter, water pump, etc., but I have not decarboned yet, plus I am using a conventional oil that I had stocked up on before reading about the advantages of switching to blends or synthetics.) Please advise.

[eurolarva]

When you replaced the fuel filter did you inspect the valve seats in the fuel pump? Two of the three are press fit and the third is held in place by two screws. You should verify the springs work on all three valves and inspect closely that the gaskets are not broken. Your problem could be coming from anywhere so this is just a guess as to where it might be coming from

[roscoe]

Do the Decarb, then clean or replace the plugs.Carbon buildup can causecompression problems and can cause detonation problems.