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  1. #1

    Default NSF15C to 20hp carb; running rich?

    Hello,

    I recently upgraded the carburetor on my NSF15C to part # 3BJ-03100-0 (20HP Carburetor) . After install and warm up, the motor seems to be running rich and begins to mis/sputter at around 1/4 throttle.

    Is there a way to tune these carburetors?

    Best,

    Anthony

  2. #2
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,674

    Default Re: NSF15C to 20hp carb; running rich?

    If the plugs are fouling, you are rich, so check them. Of course, always verify the oil level. If it's even a drop over full, you could get these symptoms. Aside from the pilot screw, the carb is not adjustable, but you could have a float/needle/seat issue.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  3. #3

    Default Re: NSF15C to 20hp carb; running rich?

    Thanks Paul,

    I did re-use one of the old carburetor gaskets. I have already ordered a replacement but have not received it yet. Otherwise the carb is brand new and Id like to avoid drilling out the brass mixture screw cap if possible. would a damaged gasket cause this?

    Best,

    Anthony

  4. #4
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,674

    Default Re: NSF15C to 20hp carb; running rich?

    Which gasket? A leaking base gasket would cause a too-lean condition.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  5. #5

    Default Re: NSF15C to 20hp carb; running rich?

    Hey Paul,

    The first gasket in relation to the carb. See below.

    Click image for larger version. 

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    I have replace with a new gasket and ensured it is seated correctly. The 20hp carb is new. I am currently testing in a tank at neutral. It seems to be bogging at around 2k RPMs and starts to blow white smoke. It doesnt bog and stall, more like bog /rev as if i were throttling up and down. I have also replaced the plugs. I know there is a chance I am hitting the limiter since in neutral but I am fairly confident that i am not.

    A bit of back story: I purchased this motor with boat about 1 month ago. The motor had been sitting for at least 2 years. When i got it home i started it for a test run and realized that it had made oil and there was a kink in the breather tube out of the crank. Both have been resolved but it did blow oil through that breather hose. Since then, i have installed a new carb (20hp), replaced plugs, and replaced gaskets.

    As stated, the motor seems to bog when throttling up in neutral (around 2-3k RPM) I plan on changing the fuel filter as well. Is there any chance this is the result of testing in neutral? (is there a fail safe or alternative rev limiter?) Also, any chance this is a residual issue caused by too much oil? I have checked compression which is good. It almost seems as if there is a delivery issue.

    Best,

    Anthony
    Last edited by awi001; 01-23-2020 at 10:48 AM.

  6. #6
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,674

    Default Re: NSF15C to 20hp carb; running rich?

    The carb base gaskets will not cause a too rich condition. Verify oil level again. If you have a tach, you should see that the rev limiter is well over 5K RPM. A clogged fuel filter could cause a lean condition at prolonged high RPM. The white smoke is probably just steam... normal in the winter. Of course, if you have a bad head gasket, bets are off, but I would think it's OK, since you have good compression. Wouldn't hurt to pull the carb and drop the bowl to verify float height.

    In general, if in N, don't run above 2K RPM, as you could damage a connecting rod, since the motor is not loaded.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  7. #7

    Default Re: NSF15C to 20hp carb; running rich?

    Thanks again Paul!

    I will check the float level.

    This is what i am currently experiencing. Youtube Link to video below

    https://youtu.be/bTKjc0ugF7M

    Best,

    Anthony

  8. #8
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,674

    Default Re: NSF15C to 20hp carb; running rich?

    Yeah. I would definitely look inside that carb, and verify oil level, and see what the plugs look like.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

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