Home Forums Tech Talk Rotax Carb problem – need help

This topic contains 12 replies, has 6 voices, and was last updated by  Steen Carstensen 4 years, 4 months ago.

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  • #26254

    Matt
    Participant

    Rotax carb, sent the motor out for re-work and the carb was reviewed and cleaned.  No real work to it otherwise as it was running fine prior.

     

    The carb pours rivers of fuel out of the small hole at the bottom of the carb, see picture, the hole being pointed at by the allen wrench.  So what is going on?  We played w/ float height, needle travel, pulled both jets out but can’t find anything that points to it.

    Thanks.

     

  • #26255

    tony zambos
    Participant

    Try pulling the carb off and dump the fuel out. Then blow into the fuel line with the carb straight up. Now turn the carb over and try blowing again. It should be harder to blow into the carb when it’s upside down because the floats are pressing the needle valve closed. Check the valve seat is screwed in all the way and the floats read “alto” when they there sitting in the bowl. The other method of checking the floats is to shake the carb and you should hear them rattle.

    LAD Specialties customer / tony kart / rotax / kt100

  • #26260

    tony zambos
    Participant

    Know you mentioned you took out both jets, but did you check it the emulsion tube for the idle jet was in?

    LAD Specialties customer / tony kart / rotax / kt100

  • #26264

    Matt
    Participant

    We did a pretty thorough check of the floats.    They do a good job of stopping fuel flow when they are installed upside down, they rattle when you shake it when installed properly.  We tried adjusting the center tab on the pivoting arms to have them shut off the fuel earlier.  With the motor running, fuel pouring out of the indicated port, we took the carb off, bowl off the bottom w/o tipping it.  Fuel level was about half way up the bowl, we were expecting that if the float is not shutting off the flow properly the bowl would be super full.

     

    We did not check the emulsion tube, don’t know what you’re describing.  All we did was unscrew the two jets, we did not take anything else out.

  • #26266

    Mike Bray
    Participant

    This is probably a dumb question but how’s the venting?  Specifically the little hose that loops from one side to the other and has a section cut out for a vent.

     

     

  • #26269

    Matt
    Participant

    This is probably a dumb question but how’s the venting?  Specifically the little hose that loops from one side to the other and has a section cut out for a vent.

     

    Winner winner chicken dinner.  I looked at that hose and thought it was damaged, threw it out, put on one that was intact.  So just now sliced a section out of it w/ a razor, started it up and no more fuel leak.

     

    Thank you very much.

  • #26278

    Mike Bray
    Participant

    There’s a reason I knew to ask that…………..

    All I’m going to say:)

     

  • #26341

    Rod Clinard
    Participant

    I too have done the exact same thing.. lol

  • #29537

    TJ Flanagan
    Participant

    Bringing this one back from the dead,  I have the same problem our friend Matt had. My solution isn’t his though, I’ve already got the hole-y hose. I’ve pulled the carb apart and everything is and blows clean.

    Any and all help will be greatly appreciated.

    -EDIT

    Since this, I’ve gotten the motor to fire up, but now the fuel just comes shooting out every orfice possible on the carb. Including the hole-y hose. I’ve got to have some type of vacuum issue somewhere, right?

  • #29554

    Matt
    Participant

    I am by no means an expert w/ these things, but by virtue of being low on the learning curve, I have been inside my son’s carb a few times recently.

     

    Have you checked that the floats are shutting the fuel flow off?  If the needle is not seating correctly perhaps the pump is just flooding fuel everywhere?  If you take the fuel tank vent hose and blow into it, what happens?  Does it get really hard to blow into or can you make fuel puke out?  The floats should close the needle which would then make it hard to blow in the vent tube.

     

    Curious what others have to offer.

  • #29558

    tony zambos
    Participant

    Pull the carb and empty out the fuel. Put a peice of hose on the fuel inlet and blow into it. Air should flow. Now, turn the carb up-side-down. You shouldn’t be able to blow into the carb if the needle valve is workiing. Make sure the floats are at the proper height and the floats are not filling up with fuel and sinking.
    Check that the floats are in the proper way. With no fuel in the carb, shake the carb up and down. You should be able to hear the floats rattle.

    LAD Specialties customer / tony kart / rotax / kt100

  • #29567

    Steen Carstensen
    Participant

    Check your needle valve. If you used carb cleaner with the needle valve in place, it will be ruined. ALWAYS remove the needle valve before using carb cleaner.

  • #26268

    tony zambos
    Participant

    Matt,
    This a link to John Savage’s article on carb prep. Page 4 has a diagram of the emulsion tube.
    http://www.rotaxjetting.com/PDFs/Documents/The%20Preparation%20&%20Jetting%20of%20the%20Rotax%20Carb.pdf

    Is there any fuel inside the floats?

    LAD Specialties customer / tony kart / rotax / kt100

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