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  1. #1

    Default Motor loses power at full throttle after 10 minutes of use

    I have a 2010 Mercury 25hp 4 stroke that I have been having problems with. At full throttle it runs fine for about 2 miles then it loses power while the throttle is at full speed. After a minute of idling, it regains power for about a half of mile. If I prime the motor while it is idling, it regains power for a short period of time. I've replaced the fuel line and connector. Does anyone know what the problem is? Any help is greatly appreciated.

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,809

    Default Re: Motor loses power at full throttle after 10 minutes of use

    Try a different fuel tank and hose. I've seen where the check valve in the bulb can lock up and stave the motor.

    Jeff

  3. #3
    Join Date
    May 2020
    Location
    Stokesdale NC
    Posts
    228

    Default Re: Motor loses power at full throttle after 10 minutes of use

    And try venting the tank, if air can't get in to replace the fuel going out then the fuel stops and the engine stops.

  4. #4

    Default Re: Motor loses power at full throttle after 10 minutes of use

    Quote Originally Posted by Fishing Mike View Post
    I have a 2010 Mercury 25hp 4 stroke that I have been having problems with. At full throttle it runs fine for about 2 miles then it loses power while the throttle is at full speed. After a minute of idling, it regains power for about a half of mile. If I prime the motor while it is idling, it regains power for a short period of time. I've replaced the fuel line and connector. Does anyone know what the problem is? Any help is greatly appreciated.

    *Update*

    I had a professional dealership have a look at my motor. They determined that the thermostat was stuck open. While the boat was there, I had them service the motor. I haven't had a chance to take the boat out and see how it runs, but I hope they fixed the problem.

  5. #5
    Join Date
    May 2020
    Location
    Stokesdale NC
    Posts
    228

    Default Re: Motor loses power at full throttle after 10 minutes of use

    It sounds like you needed the t/stat whatever happens but that wouldn't make the engine bog down like your describing. We will hope for the best for you.

  6. #6
    Join Date
    May 2013
    Location
    TX.
    Posts
    404

    Default Re: Motor loses power at full throttle after 10 minutes of use

    This is July....... Stuck closed thermostat...... yes a problem. Stuck open and that causing any kind of a problem???????? Engines ran for decades without stats, just free flow cooling water. Agree with Swagonmaster on tank not venting properly.

    Engine fuel pump suction is only a slight vacuum. It can only lift so much fuel, so fast. If the tank isn't vented once that small vacuum migrates to the entire fuel source (the tank volume), fuel can no longer flow to the engine. Your stopping and restarting comment suggests that the vent, and for that engine you're probably running on a portable tank, which would be in the lid of the tank, probably partially closed/obstructed...it happens. Your squeezing the bulb and getting positive results supports this assumption. Removing the cap and running would answer the question immediately. Compressed air and a small piece of wire should open it back up.

  7. #7

    Default Re: Motor loses power at full throttle after 10 minutes of use

    Quote Originally Posted by Texasmark View Post
    This is July....... Stuck closed thermostat...... yes a problem. Stuck open and that causing any kind of a problem???????? Engines ran for decades without stats, just free flow cooling water. Agree with Swagonmaster on tank not venting properly.

    Engine fuel pump suction is only a slight vacuum. It can only lift so much fuel, so fast. If the tank isn't vented once that small vacuum migrates to the entire fuel source (the tank volume), fuel can no longer flow to the engine. Your stopping and restarting comment suggests that the vent, and for that engine you're probably running on a portable tank, which would be in the lid of the tank, probably partially closed/obstructed...it happens. Your squeezing the bulb and getting positive results supports this assumption. Removing the cap and running would answer the question immediately. Compressed air and a small piece of wire should open it back up.
    You guys were right. I took the boat to the river today and had the same problems. I replaced the fuel tank, new fuel line, connectors, and primer bulb. The motor runs fine. The only problem is it loses power after 5 or 6 miles of riding. Whatever it is, it isn't major. Just aggravating to find.

  8. #8
    Join Date
    May 2013
    Location
    TX.
    Posts
    404

    Default Re: Motor loses power at full throttle after 10 minutes of use

    Quote Originally Posted by Fishing Mike View Post
    You guys were right. I took the boat to the river today and had the same problems. I replaced the fuel tank, new fuel line, connectors, and primer bulb. The motor runs fine. The only problem is it loses power after 5 or 6 miles of riding. Whatever it is, it isn't major. Just aggravating to find.
    Squeeze the bulb when it starts slowing down....what happens? Is the bulb soft.....obvious there is fuel in it or collapsed...flat when you squeeze it?

  9. #9

    Default Re: Motor loses power at full throttle after 10 minutes of use

    Quote Originally Posted by Texasmark View Post
    Squeeze the bulb when it starts slowing down....what happens? Is the bulb soft.....obvious there is fuel in it or collapsed...flat when you squeeze it?

    When I squeeze the bulb, it is soft. After idling for a minute, it regains power. I'm lost. Plus it is getting expensive to find the problem. I need help!

  10. #10
    Join Date
    May 2013
    Location
    TX.
    Posts
    404

    Default Re: Motor loses power at full throttle after 10 minutes of use

    Quote Originally Posted by Fishing Mike View Post
    When I squeeze the bulb, it is soft. After idling for a minute, it regains power. I'm lost. Plus it is getting expensive to find the problem. I need help!
    You squeezed the bulb....when, idling? " After idling for a minute it regains powe"....what idling, or you were back up and running? Did you pump the bulb while up and running while it acted up....in short, you used the bulb as a fuel pump bypassing the action of the engine's fuel pump with squirts of fuel filling the carb. bowls so that the engine could run off it and if so, did it pick up or no change?

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