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Tohatsu m40c stalls under load

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  • Tohatsu m40c stalls under load

    Maybe someone can shed some light on this issue.

    Tohatsu m40c dies under load. The following has been done and I will try to explain symptoms.

    Motor runs great on the muffs or in a bucket. Motor will run at any rpm in neutral for as long as you want it to.

    Compression is 140 per cylinder and spark is good. Gas is new, fuel pump looks good when taken apart. Timing is spot on

    When you put the boat in the water it fires right up, back off the trailer, idle out and when you take off it makes it about 12 miles an hour then starts to die. Primer ball stays hard, pumping it doesn't save it, straying carb cleaner at it while it dies doesn't help. Bumping choke actually makes it worse.

    Almost like when it gets a load on it there is to much fuel or fuel/air mixture is off.

    If motor does stall you can bring it back to idle and it starts right back up.

    Carb was supposively gone through by a tech and was spotless. Intersting that if fuel related it can't be saved by carb cleaner.

    Tried straying cleaner on visible gaskets, no obvious leaks/ increase.

    Any ideas?

  • #2
    Still sounds like a carb/fuel issue.
    Buffalo NY USA


    • #3
      Sign up today
      If tank and internal mesh filter are clean, fuel pump & carb are immaculate clean symthoms could be due to :

      -Was tank's air valve opened during test ? Are fuel pump's diaphragms in good shape ?

      -Being an oldie, fuel connector's o'rings could be dried, hardened, let air in into fuel line and OB stats to miss worse when giving throttle. Test with a new fuel hose or one in opt working state.

      -Could be a heat realeted issue building up on any internal electrical/electronic component, which are hard to diagnose compared to diagnosing fully kaputt same parts. Timing advance is set to how many į

      -One story is at idle on muffs, water, other at load....

      Happy Boating
      Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers