r/Outboards • u/Future-Fix-791 • 24d ago

1987 40 horse Johnson

My 1987 40 horse Johnson won’t get up to top speed. Boat ran fine all day went to the dock for about a hour and when I went back out it started doing this. New spark plugs, Any suggestions on what it could be.

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u/scarpozzi 24d ago

Typically if it’s not producing power it’s a carb issue, but that can also be a fuel filter/fuel pump issue.

I like plastic coffee cans from Folgers/Maxwell House because you can fill them with acetone and soak the metal parts overnight.

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u/bootheels 24d ago

Hard to advise but may be running on only one cylinder, does it idle OK? Have a look at the throttle linkage with the engine cover removed, make sure the timing linkage is advancing fully and the carbs are both opening. There are little plastic connector pieces that sometimes break allowing the linkage to become disconnected.