Merc 25HP Four Stroke Problem

Hi Randy,
I am having problems with my 25 HP four stroke Big foot mercury outboard engine.
It started at the end of the season, it starts, idles and will travel at low rpms but when you get above 2400 it starts cutting out and sometimes missing so badly that it dies.

I have checked the fuel filter, checked all of the fuel system for air leaks, have run injector cleaner through it, and cannot get it to stop missing.

Any ideas?




We get stuff like that every year after the boats come out of storage. Most likely the carb is gummed up. The passages and orifices are so small in the 4-strokes that they plug very easily. Clean it out and the problem should go away (you will have to disassemble it to clean it).




Please submit whatever questions you have to  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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