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  1. #1
    Join Date
    Oct 2011
    Location
    New Zealand and Colorado
    Posts
    23

    Default Tohatsu small 2-stroke - Tricky diagnosis

    One week ago, the Tohatsu 8hp 2-stroke started and ran well. Now she won't.

    What really puzzles me is:
    - She does not respond to starting spray into the carb (no reaction at all), but ...
    - She will run smoothly and confidently for 5sec when fuel is sprayed directly into a cylinder via a spark plug hole.

    My first thought was that the only thing that could block starting spray in the carb from getting through, are bad reed valves.
    So I took off the carb and removed the reed valves - they look perfect, springy and seal well. So it's not them.

    That's where I am now. Not sure what to try next - need help.

    Extra Background:
    Non-starting symptom appeared after dropping the lower leg, replacing the impeller, transporting her in the boot of a car for a day, on her back.
    When refusing to start, I did the usual :
    - fresh fuel and clean fuel line
    - rebuilt carb with clean jets, float good, float needle valve good
    - compression tested ok
    - new plugs, good blue spark (jumps 5/16 air gap with plug tester)

    The fact that she will run smoothly and confidently when fuel is sprayed directly into a cylinder suggested to me that
    the electrics are likely ok.

    Click image for larger version. 

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    Click image for larger version. 

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  2. #2

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    Yes that sound that is a problem with fuel if it works when you spray fuel directly

  3. #3
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    15,251

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    It ran a week ago.-----What happened ?----Did it quit while running ?----Slowly died out ?----Possibly water in the fuel / carburetor ?

  4. #4
    Join Date
    Oct 2011
    Location
    New Zealand and Colorado
    Posts
    23

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    Racerone - ran fine, then laid down and lower leg removed for impeller replacement When mounted again a week later, no start.

    As mentioned, will run smoothly when fuel sprayed into cylinder, but NOT when fuel sprayed into carb throat or even with carb removed, into intake manifold.

  5. #5
    Join Date
    Mar 2010
    Location
    Buffalo, NY, USA
    Posts
    2,248

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    possible poor crankshaft seal.
    Paul
    Buffalo NY USA

  6. #6
    Join Date
    Oct 2011
    Location
    New Zealand and Colorado
    Posts
    23

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    Thank you Pvanv, did not think of that, but it makes good sense.

    I don't have Leak-down test equipment - so is there any other way(s) to check on how well/poorly the crankshaft seals are sealing in a small 2-cyl outboard, without disassembling the powerhead and crankcase?

  7. #7
    Join Date
    Mar 2010
    Location
    Buffalo, NY, USA
    Posts
    2,248

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    Given that you verified that it runs when fuel is in the cylinder... it runs. Given that adding fuel to the inlet does not make it run, then that fuel is not getting to the cylinder. Hence the possible seal issue. The other possibility is... if there is an accumulation of unburned two-stroke oil that was pooled in the bottom of the crankcase, then laying the motor down could have caused that to slop around, being basically un-burnable sludge, that could stop running. It might be good to see if you can clear out the crankcase... maybe with mineral spirits or acetone (or both) and re-try running with fuel at the carb.
    Paul
    Buffalo NY USA

  8. #8
    Join Date
    Oct 2011
    Location
    New Zealand and Colorado
    Posts
    23

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    Really appreciate the advice, Paul.
    Thinking about it, once the problem arose, I have pulled the starting cord dozens of times (maybe even a hundred) and, since it was not firing, there may well have been a good amount of two-stroke oil deposited into the crankcase.
    I have noticed big drops of oil coming out of the prop when I attempt to start it, but assumed it is normal - just the 2-stroke oil left over after the gasoline evaporates subsequent to unsuccessful starting attempts.
    I did not know that such an oil deposit sloshing around in the crankcase can have an impact on starting, so this gives me a useful lead to pursue, thanks.

  9. #9
    Join Date
    Mar 2010
    Location
    Buffalo, NY, USA
    Posts
    2,248

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    If it's dripping from just pulling the starter, it's loaded with unburned 2-stroke oil.
    Paul
    Buffalo NY USA

  10. #10
    Join Date
    Oct 2011
    Location
    New Zealand and Colorado
    Posts
    23

    Default Re: Tohatsu small 2-stroke - Tricky diagnosis

    So I have squirted some gasoline into the crankcase and closed up for a couple of days to allow any oil sludge to dissolve, and can now report that the motor is firing again - not perfectly yet, but will do some carb cleaning and adjustments and think it's going to end well.
    .
    Thanks Paul for your input at a point where I had run completely out of ideas (I owe you a quality lunch if I travel through Buffalo NY).

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