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rotax 582 bing 54 carbs high end revs query

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  • rotax 582 bing 54 carbs high end revs query

    I have a new rotax 582 greyhead with bing 54 carbs. I ran the engine in a year ago,no problems -It revved cleanly to 6500 rpm. I did not use it for a year. This year I have moved to sea level from about 700m where it ran last. Fuel is now 95 gasohol, not petrol only as I cannot buy that now. The engine runs cleanly to 6000 rpm, but seems to get starved of fuel after that, coughs and splutters between 6 and 6500. I checked the fuel line and changed the fuel filter, and set up the mechanical carb balance, sliders moving in synch and wide open when throttle fully open. I dont think it is dirt in the carb?. Anything I can check before dismantling the carbs to clean- Adjust fuel mixture, needle height? I would not have thought 700m altitude difference would cause it. Would gasohol fuel cause this?
    Last edited by Brian Blackwell; 26th July 2020, 15:56.

  • #2
    One thing that I have found is that using mogas is that it has cleaning agents in it. Thus if you have any deposits or built up emulsions on the metal work these agents clean these from the surface. They are then in circulation and ready to cause full or partial blocking. Plus of course there can be the well know problem of water absorbsion into the fuel.
    You may find this site useful

    The jetting chart on the same site gives info on adjustments, here

    I hope that helps


    • #3
      Much appreciated.


      • #4
        The other thing to check is the vacuum fuel pump. First of all make sure it's the round type Mikuni, the one with dual outlets, and not the rectangular type. Next, make sure it's working correctly, and that the vacuum tube that runs from the side of the crankcase to the pump is in good condition and doesn't have any leaks.

        I had symptoms similar to yours once with a 462 engine that I put on a trike that had previously had a 447. The rectangular fuel pump as fitted to the trike was perfectly adequate for the 447 at full chat, but wasn't passing enough fuel for the 462 when I gave it full throttle. I had to change the fuel pump to the round type Mikuni, and once I'd done that it worked perfectly.

        There is also the thing about the Mikuni round pump that it should ideally be mounted horizontally. If it's mounted vertically then check to see if there's a really tiny hole in the metal thing at the back that the vacuum tube connects to. If that gets blocked then moisture will build up in the pump and can cause the diaphragms to stick.
        XL's forever! Well, one of them anyway. It's all I can afford, not to mention the Raven and the Mini-Max. Oh, and I almost forgot the Spectrum as well :-)