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  1. #1

    Default Losing power after running full throttle. (Even after cleaning carb)

    I'm baffled by my 3.5 mercury 4 stroke. The ongoing problem is that it runs fine for maybe 15-20 minutes on full throttle then it starts shutting down and won't run any higher than half throttle.

    Spent yesterday working on it. New spark plug, changed the oil, and most importantly disassembled the carb blew carb cleaner in every hole and let sit for an hour before blowing out with air and reinstalling. It looked clean to the eye from the start but I still thought that would fix her. Not so.

    I have no idea what to do next. Please help.

  2. #2
    Join Date
    Dec 2015
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    maplevalley WA
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    3,469

    Default Re: Losing power after running full throttle. (Even after cleaning carb)

    Have you tried running with the fuel cap loose do you have the vent open?
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  3. #3

    Default Re: Losing power after running full throttle. (Even after cleaning carb)

    Quote Originally Posted by kimcrwbr1 View Post
    Have you tried running with the fuel cap loose do you have the vent open?
    Vent is open. A few times I have opened the cap to check fuel level and nothing changed.

    I wonder if if it could be overheating since it happens after running for a bit then gets better after the engine sits. It's pissing water like a hose at high rpm though so I would imagine it's getting the water it needs.

    How is would I fix/check for overheating?

  4. #4
    Join Date
    Dec 2015
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    maplevalley WA
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    Default Re: Losing power after running full throttle. (Even after cleaning carb)

    Do you flush the engine after each use with tap water? The best way is when you get home put it in a barrel of water and run it for a few minutes and then turn off the fuel and let it run out of gas. You can try running in a barrel of water with salt-away for 1/2 hour or so and see if it makes a difference. Fresh water still has alot of silt and minerals that builds up flush it regularly and allways store it in the running position so it has a chance to drain out completely.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  5. #5

    Default Re: Losing power after running full throttle. (Even after cleaning carb)

    There was a time with this motor where I didn't know to do that but lately it's been getting fresh water flushed every time. Do you think there could be buildup that a few hours on a fresh water lake isn't washing out? How would I check? Could salt and not flushing have messed anything else up that would cause the symptoms mentioned?

    I really appreciate the input from everyone.

  6. #6
    Join Date
    Dec 2015
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    maplevalley WA
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    Default Re: Losing power after running full throttle. (Even after cleaning carb)

    Get a gallon of salt-away and give it a good flush in a barrel for at least 1/2 hour at high idle in gear. Other than taking it apart that is the best you can do. Lake water has alot of minerals and silt you should always flush it in a barrel with tap water after each use will keep the circuits clean.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  7. #7
    Join Date
    Dec 2015
    Location
    maplevalley WA
    Posts
    3,469

    Default Re: Losing power after running full throttle. (Even after cleaning carb)

    Its about $50 a gallon at walmart if you use a small barrel you can mix 1/2 gallon salt-away and just let it do its magic.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  8. #8
    Join Date
    Sep 2008
    Location
    Hague, Virginia, USA
    Posts
    3,670

    Default Re: Losing power after running full throttle. (Even after cleaning carb)

    First check for overheating. Run the engine until it revs down, then take off the cover and check the head with an infrared heat gun. I think the heads should read about 160 F, but check that. If substantially over that, then it's overheating. If not, it's likely something else.

    If you have one of those see-through fuel filters on that engine, check for air bubbles in it. BTW - when was the last time the fuel filter was changed? It should be changed every season as a minimum.
    CHawk 25 DLX

  9. #9
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,758

    Default Re: Losing power after running full throttle. (Even after cleaning carb)

    Built in fuel tank ? every check it for sediment accumulation?

    When was the last time the spin on filter was changed?

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