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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4717
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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I have a 2005 F40 four stroke Yamaha outboard and the carbs

Customer Question

I have a 2005 F40 four stroke Yamaha outboard and the carbs constantly clog. I change fuel regularly, put in an additive, run the carbs dry after use. I use the engine so infrequently that the fuel is never any good. It was suggested that I change my fuel jets to one that have larger openings. Converting to F25LA's was suggested. Would this work or should I change then to a something else? Why would F25's have larger openings than F40's? Bot***** *****ne, other than what I mentioned above is there anything that I can do to prevent this problem. Also, my fuel jets are clogged now.
Is there anything I can do to clean them without removing them?
George Kuper
Submitted: 1 year ago.
Category: Boat
Expert:  Jeff G. replied 1 year ago.
George, we need to look at things a little differently.Changing jets would not help at all. Your problem isn't just the fixed jets but all the little orifices in the carb. Changing the size of the jets will only cause the engine to run poorly, if at all and you'd still have the same problem.Running the carbs dry after use is also harmful. First of all it leans out the fuel mixture which can damage the engine. In addition you don't actually run the carbs dry, you run them until they lean out from fuel starvation. There is still fuel left in the float bowl to foul and clog the carbs!Here is what I would recommend; Run the engine with a fuel treatment and stabilizer. You may also want to run with some Ring Free in the fuel to keep the fuel in better condition.If you run it that infrequently then use a little fogging oil sprayed into the air intake when you flush the engine. After choking the engine with the fogging oil manually drain the carbs. On the bottom side of the float bowls is a drain screw. Put some paper towels under the float bowl, open the screw and manually drain. This way there isn't any fuel in the carb to go bad.I would also dump any fuel older than 30 days old. Run it in your lawnmower etc. Start out the next trip with all fresh fuel.Doing these simple things and you will not have a stale fuel, clogged carb problem.As for your jets now only a good cleaning and rebuild will do. As I said the high speed jets aren't the only thing that gets clogged. Not cleaning properly and you run the risk of damage to the engine.Please post back with any further questions.Thanks

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