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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 2003 Merc 9.9, 4 stroke, with carb. It has always

Customer Question

I have a 2003 Merc 9.9, 4 stroke, with carb. It has always run great up until now. I started it for the first time this spring yesterday. It starts right up and runs for about one minute fine and then begins running rough at all speeds even after it has warmed up. Pulled plugs, cleaned them, installed them and went thru the same sequence again twice more. Same pattern. The fuel was fresh as of last October but has been sitting in the tank since. I have been using an additive in the fuel that is supposed to combat the alcohol problems. The 115 horse Merc, 4 stroke, fuel injected motor starts and runs fine on the same gas. I haven't changed the fuel filter since 2013 so I have that on my list of things to do. I'm also wondering if it could be the fuel pump (alcohol related deterioration of the diaphragm)? Any ideas on where best to start.
Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.
Hello Dave, my name is***** will assist you.The fuel pump could be falling apart inside, that is a place to start looking. It could also be the fuel lines going to the engine. If they are gray, with red writing on them, i would remove one end of the line and look down inside it to see if it is coming apart. How is the oil level in the engine?Is there any water in the fuel?

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