Carby Engine randomly speeds up and slows down at full throttle

Discussion in '2-Stroke Engines' started by skinnerman, Jul 27, 2014.

  1. skinnerman

    skinnerman New Member

    Hiya, ran in a little more trouble.

    When at full throttle, the engine will suddenly slow down, them speed up, then slow down etc, so I have to run it at
    3/4 throttle to keep it from doing that. I think it has to do something with the air/fuel mixture getting screwed up at
    high RPMs. Also my airfilter is soaked with this brownish oil.

    Any suggestions?

    Running it at 25:1

    How do I know whether it's rich or lean? How can I get the best out of the A/F mix?

    Last edited: Jul 28, 2014

  2. Fabian

    Fabian Well-Known Member

    You read the information contained in the weblink, and once you've read it "completely", you then read it twice more, before even assembling or riding your motorised bicycle.
  3. crassius

    crassius Well-Known Member

    loose engine mounts will cause the carb to vibrate & foam your fuel to cause this
  4. skinnerman

    skinnerman New Member

    YES! I can see this in the fuel line it's usually always foamish. It probably does the same thing in the carb float container.
    But the problem is all my mounts are as tight as I dare make them. Would air in the fuel line/filter make the problem worse?
  5. crassius

    crassius Well-Known Member

    getting the mounts tight is not always the same as getting the nuts tight on the studs - see if you can hold the frame and push the motor left or right - your mounts may not be straight enough to grip well
  6. skinnerman

    skinnerman New Member

    The engine is locked on the bike. It's not going anywhere and I can't push it at all.
    I'm using the T bracket.
  7. KCvale

    KCvale Motorized Bicycle Vendor

    Poor fuel flow will cause this, you are using more fuel at WOT than your fuel system can deliver.
    The screen filter in the tank can cause this, so can a clogged in-line filter.
    skinnerman likes this.
  8. skinnerman

    skinnerman New Member

    Okaydokey I will check on that. Thanks!