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  1. #1

    Question Nissan NS5B two stroke leaks fuel when tilted

    Our year 2000 Nissan 5hp two stroke now leaks gasoline from the front of the carburetor (carbi) when tilted up on the dinghy transom. This started after 7 years of not leaking. The leak is at the opening at the choke flap.
    It leaks only when fully tilted.
    It leaks only when there is gas in the carbi bowl.
    It leaks even when the gas line from the tank to the fuel pump is disconnected at the fuel pump. That removes any connection between the internal tank and the carbi.
    It leaked after we replaced the carbi bowl gasket (o-ring), float, needle, spring, drain screw washer. So then....
    We replaced the entire carbi with a branClick image for larger version. 

Name:	Nissan 5hp carbi leak1.jpg 
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ID:	20940d new one (which includes the fuel pump) and it still leaks!
    It did not leak in the past when tilted.
    Although manufactured in year 2000, motor wasn't really used much until 2011 and from then used regularly, but not heavily. It runs perfectly and starts on the 2nd pull. There wasn't any other event I can think of that coincided with it starting to leak when tilted. We just began to notice fuel on the inside of the transom.
    The photo shows the leak at the air inlet. The fuel pools a bit right at the edge and appears dark in the photo.
    We welcome any suggestions about the possible cause; really thought replacing the carbi would solve the problem.

  2. #2
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,518

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    Shut off the fuel valve before tilting. The fuel in the bowl will still run out. Normal.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  3. #3

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    Quote Originally Posted by pvanv View Post
    Shut off the fuel valve before tilting. The fuel in the bowl will still run out. Normal.
    Hi Paul,
    Yes, I always shut off the fuel valve before tilting. In past 7 years we've been tilting the motor in exactly the same fashion without any fuel leaking from the carbi. Now, it actually drips out and into the dinghy when tilted. (We do not run all of the fuel out of the carbi before shutting down). Something, somewhere has for the fuel to leak when tilted.

    All is a bit of a mystery.
    David

  4. #4
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,518

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    If you run the carb dry, that will not happen. Think of a teacup turned to a 45 degree angle.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  5. #5

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    Quote Originally Posted by pvanv View Post
    If you run the carb dry, that will not happen. Think of a teacup turned to a 45 degree angle.
    Hi Paul,
    That is certainly true--run it dry and it does not leak. The thing is we are out cruising and use the dinghy to go from the boat to shore a couple of times a day when we are at anchor. While at shore and at the boat we always tilt the motor to prevent corrosion (we're always in salt water).
    That makes it pretty inconvenient to run the carbi dry each time before tilting. (The instruction manual doesn't mention running dry before tilting.)

    As I mentioned, until recently the motor has not leaked when tilted without running it dry. I always close the fuel cock and the air valve on the top of the internal tank.

    The absence of the leak over the past seven years and then for it to suddenly start occurring every time the motor is tilted is really creating the mystery for me; it seems to defy engine logic.

    Would you have any contact information for Tohatsu folks in Japan we could query?

    Thanks, David

  6. #6
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,518

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    I have info for Tohatsu America, but not in Japan.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  7. #7
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,518

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    You need to understand that ANY carburetor will dump gas if you turn it 45 degrees. If the starboard side is up, odds are it will only drain the bowl.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  8. #8

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    Hi Paul, Perhaps you could help me understand why for 7 years the motor did not leak gas when the engine was tilted up. As I mentioned before, it has only recently started to leak.
    I think it is unlikely that Tohatsu designed, built, and sold a motor that leaks fuel when it is tilted. If the company had done so, the instruction manual would certainly warn that the fuel must be removed before tilting.
    If you have a motor available perhaps you could test the tilt function with fuel in the bowl of a 5hp two stroke?

    After July 9, I'll postpone the trouble shooting for a couple of weeks. We're a Seattle boat, but now in Brisbane bound for Suva on the 9th.
    Thanks, David




    Thanks, David

  9. #9
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    2,518

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    It so happens that I have a 5B in the shop. I'll check.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  10. #10

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    Hi Paul,
    Thanks for following up on this mystery. I look forward to learning what you discover.
    David

  11. #11

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    Paul, our weather window for departure to Suva vanished on the 8th so we're still in Brisbane.
    Have you gathered any further information on the fuel leak when the 5 hp is tilted? We really appreciate your help with this.
    David

  12. #12

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    I had the same thing happen with a NS3.5A.
    For many years we tilted it up without shutting off the fuel....no leaking.
    More recently, the tank gets emptied if the engine is tilted.
    Never figured it out.

  13. #13

    Default Re: Nissan NS5B two stroke leaks fuel when tilted

    So, with your NS3.5A does the fuel leak from the carburetor when tilted and when the fuel valve is closed? We have always closed the fuel valve and it never leaked until recently. Now it leaks when tilted even with the fuel line disconnected so something unrelated to the fuel tank, valve and hose has changed.

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