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Thread: Yamaha 25 problem??

  1. #21
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    Quote Originally Posted by Luvin' Labs View Post
    Check compression and leak down. My motor would do that to. Would let it idle or sit for a bit, and then it would run fine again. I thought my issue was trash in the carb or something along those lines. Come to find out is bad compression/leak down.
    Talk to me more about this. What is leak down? If bad compression, does that mean the motor is shot? Appreciate all the help

  2. #22
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    Use a compression tester to test for adequate and even compression. You can get a kit from an auto parts store. It’s a good tool to have. Should be from 125-150 psi. If it comes back low, you can buy de-carb spray and see if that helps. It pretty much cleans any carbon build up. Directions say to spray it in the air intake side of the carburetor, for a 25hp, 2cyl, you will probably need to spray into the spark plug holes and the turn the engine over as well due to the intake being vertical. There is a lot of literature online about it. Check the hull truth to start. (That is if it comes to it).
    Last edited by cam1195; 07-06-2020 at 10:25 PM.

  3. #23
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    This straight from Wikipedia but it has the info you need.

    https://en.m.wikipedia.org/wiki/Leak-down_tester

  4. #24
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    check your fuel line inner core may be collapsing

  5. #25
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    Compression on that motor is likely more around the 110psi mark, possibly a tad lower. From what I recall std compression on a stock 3cyl 40/50 is 115ish.

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    Last edited by willyworm; 07-07-2020 at 07:56 AM.
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  6. #26
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    Quote Originally Posted by nsantee View Post
    check your fuel line inner core may be collapsing
    Have just changed fuel lines. I was convinced that’s what it was.

  7. #27
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    Betcha got a coil breaking down due to old age and heat.

  8. #28
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    Quote Originally Posted by Model12 View Post
    Betcha got a coil breaking down due to old age and heat.
    I looked online to see how to check that and it doesn’t look too hard. I bought a compression Gauge. Will check that tonight. I guess a bad ignition coil would be an easier And cheaper fix than low compression. I really love this old motor. It will push my ear eagle 1542 at 32-33 when it’s running right. It’s perfect for the boat

  9. #29
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    I'm still guessing it is over heating. If it sat for 15 years my money is on the impeller being dry rotted.

  10. #30
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    Quote Originally Posted by ColumbiaCornbread View Post
    I'm still guessing it is over heating. If it sat for 15 years my money is on the impeller being dry rotted.
    Water pump was the first thing changed. No issue with that at all. Keep in mind, it’s been up and running for the last 2 years. This problem has been over the last 6 months.

  11. #31
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    when it starts acting up, shoot the head and water jacket with a cheap temp gun from harbor freight and see what temp is. If its running cool, its most likely an ignition coil as previously stated.
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  12. #32
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    How long do you have to wait for it to run normal again? Also, does it do it when you are running wide open at 45 minutes or only when coming off plane/at idle and then revving back up or trying to get back up to speed?

  13. #33
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    Quote Originally Posted by Elcid_Fowler View Post
    How long do you have to wait for it to run normal again? Also, does it do it when you are running wide open at 45 minutes or only when coming off plane/at idle and then revving back up or trying to get back up to speed?
    It takes a while to start back to normal. Not sure exactly because I generally just limp back to the landing and put it on the trailer. The power loss occurs when I’m up and running. So I will be planed off running fine and it will just power down. It won’t cut off, it just powers down. After that, I can feather the throttle to just barely get it back on plane. If I power up too far, it will totally bog down again.

    Didn’t get to test compression last night bc of baseball practice. Hope to get to it tonight.

  14. #34
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    So I checked compression. Engine was cold. Not sure if I was supposed to have it warm. Checked an even 100psi on both cylinders. Is that good? Bad?

  15. #35
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    Sounds like its overheating and limp mode is kicking in. Temp gun sounds like the way to go. Did you replace the housing and impeller or just the impeller? My bet is its your water pump.
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  16. #36
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    Quote Originally Posted by justpracticin View Post
    Sounds like its overheating and limp mode is kicking in. Temp gun sounds like the way to go. Did you replace the housing and impeller or just the impeller? My bet is its your water pump.
    It’s peeing great. I replaced everything that came with the kit. Couple years ago, I can’t remember if it included the housing or not. Also, if it means anything, the water coming out is cool to the touch

  17. #37
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    I would replace the pump again. I had someone else put a new one put in a 40 last year and it failed this year. Similar MO to yours, ran great for a while, cut into limp mode, let it cool completely and it would run great again. Replaced impeller and housing and it has done great since. It was peeing fine the while time.
    Last edited by justpracticin; 07-09-2020 at 01:31 PM. Reason: adding piss note
    Honey...I'll do it after the season is over.


    Originally Posted by cudexter
    I would argue that JP has the highest "quality" to "trash talk" post ratio on this site.

    Quote:
    Originally Posted by Air Raid
    ... Wait till 3 years from now! ...



  18. #38
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    If you feel pretty confident in the housing and impeller to check that off the list I would do like someone else mentioned and remove the thermostat and run it hard for an hour or so. It may be a little harder to get warmed up but it will. You might blow some trash out of the system that's been caught in there.

    Any response is welcome if you think this is a bad idea.

  19. #39
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    Quote Originally Posted by justpracticin View Post
    I would replace the pump again. I had someone else put a new one put in a 40 last year and it failed this year. Similar MO to yours, ran great for a while, cut into limp mode, let it cool completely and it would run great again. Replaced impeller and housing and it has done great since. It was peeing fine the while time.
    That’s interesting. How did you diagnose that problem? Or you were just guessing??

  20. #40
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    I knew it was a temperature dependent. Figured coil or water pump. Water pump is a maintenance item anyway, so i tried it first. Guess I got lucky.
    Honey...I'll do it after the season is over.


    Originally Posted by cudexter
    I would argue that JP has the highest "quality" to "trash talk" post ratio on this site.

    Quote:
    Originally Posted by Air Raid
    ... Wait till 3 years from now! ...



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