48 cc "Yawning" problem

Discussion in '2-Stroke Engines' started by WillieB, Jun 2, 2011.

  1. WillieB

    WillieB New Member

    "Yawning" is the best way I can describe it. I'll be running along nice and fine at WOT and all of a sudden engine pitch changes to the "yawn." In fact it sounds just like releasing the clutch without the fuel on. If I throttle down, the engine picks back up and runs just fine again.
    Have any of you run across this and what could be causing it?

  2. rustycase

    rustycase Banned

    Sounds like some sort of fuel related problem.

    Really should NOT be on extended WOT runs until it is resolved.
    (and I realize that is a difficult thing to ask, when running micro-motors!)

    ..could need jetting adjustment.
    ..Float in carb could need adjustment.
    ..fuel supply could be restricted.

    What does the plug look like?
    What is the air temp/engine temp when this happens?

    Good luck
  3. srdavo

    srdavo Active Member

    I've had the same symptoms, on a couple different bikes.

    The choke was the culprit. The lever on the carb was loose & the engine vibration would cause the choke to close & open at will. So when the choke vibrated closed I would get the 'yawn'.
  4. WillieB

    WillieB New Member

    thanks, I'll look into that
  5. wackey101

    wackey101 Member

    rusty case is right you also would want to tune your engine you must find out if your runing to rich or lean that is the main thing and check for old fuel thats is the culprit sometimes and other like rusty case told you
  6. motorpsycho

    motorpsycho Active Member

    your float level could be set too low.
    if your carb is at an angle the float bowl could be running out of fuel due to the angle. your fuel filter could be plugged up restricting the flow of fuel into the carb.
    the float bowl could be going empty faster than gravity can re-fill it (or keep it full). this could be a foat adjustment problem, a fuel flow problem, or a carb angle problem.
    the carb needs to be as level as possible.
    also the air-fuel ratio could be way lean and this would cause the exact same "yawn" problem at w.o.t.