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  1. #1

    Default Cant shut off motor - Revs High

    Ok i just started my motor up to get it ready for the season. It is a 40 hp evinrude. It was oil injected but that has since been bypassed so it runs off mixed.

    The motor starts and runs good, but when I give it a decent amount of throttle, the motor takes off reving up, going Wide open throttle. And even if I pull the throttle back to neutral, it still goes full throttle. The key wont even shut off the motor when it does this. The only way to shut it off is to pull off the gas line.

    I can start the motor again and it runs fine at less than half throttle. And, I can use the key to shut it off too. But as soon as I go past half throttle, the motor "takes off" and can not be controlled or shut off anymore.

    The cables move freely, the throttle plates open and spring close smoothly, I sprayed carb cleaner to loosen any gunk, but it wasnt really dirty.

    The only thing that i can think of it the gas. It is gas from last year. I dont know if that could make it do that or not. I still wouldnt undertand why i cant shut off the motor with the key.

    If anyone has any ideas or can help in any way I would be greatly appreciative. I'm dying to get out on the water

    Thanks, Tim

  2. #2
    Supreme Mariner
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    Jul 2006
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    Florida Gulf Coast
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    19,308

    Default Re: Cant shut off motor - Revs High

    Let me guess, you are running it out of the water, right? Or at least you are revving it up in neutral or with no load on the prop--right?

    Don't do that!!!!

    It is called thermal run-away or Dieseling, or whatever you want to call it. Run it like it was designed to run, on a boat in on the lake, and don't over rev it in neutral, and I'll bet it won't have that problem.

    EDIT: PS, I was going to ask if it was made by Toyota, but I won't.

  3. #3
    Vice Admiral
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    Default Re: Cant shut off motor - Revs High

    That's why, if you read some more posts here, there is always a warning to not rev up your engine when on a hose adapter or in a barrel, or really anytime when not loaded (e.g. in neutral). You can easily destroy the engine that way. The only way to shut it down is to remove the gas or choke it out. Throw a towel in the carb throat and it will shut off the air.

    When it's in a runaway condition, even pulling off the spark plug wires will not shut it off. The motor has turned into (kind of) a 2-stroke diesel....

  4. #4
    Petty Officer 1st Class
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    Mar 2010
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    South East Pa/ Chesapeake, MD
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    Default Re: Cant shut off motor - Revs High

    How can it rev up if the throttle is pulled back? Doesn't that force the baldes closed in the carbs?

    Or does engine vacuum keep them open? Just curious!

  5. #5
    Chief Petty Officer cedarjunki's Avatar
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    Aug 2007
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    plattsburgh area
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    471

    Default Re: Cant shut off motor - Revs High

    sucking air around carb.... make sure oil injection line is plugged off!
    possibly the crank seals are bad sucking too much air..

  6. #6

    Default Re: Cant shut off motor - Revs High

    Thanks guys. So your saying that If I take it out on the water i should be fine? Im just scared it will happen out there and I wont be able to stop.

  7. #7
    Vice Admiral
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    Default Re: Cant shut off motor - Revs High

    If you have been revving it up with no load on it, then it will go into runaway. It will not happen in gear on the water.
    They are many more things to be afraid of on the water than that.....

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