Carby lost power after carb upgrade

Discussion in '2-Stroke Engines' started by imacf90, Dec 7, 2014.

  1. imacf90

    imacf90 New Member

    so i just recently built my first motorized bicycle. I'm still in the break in period, but this really bothers me. so.. after upgrading to a better carburetor, i noticed a significant loss of power. from what i've read its one of those chinese clone performance carbs(the dax RT carb). i don't use the choke. it always bogs down and that initial 'push' wont disengage it. my top end has lowered by quite a bit. i've had to set the idle screw all the way in to get a decent idle, otherwise it stalls. everything is regularly tightened back up after i ride a few times. it was just more lively with the old, more restrictive carb. why would that happen?

    I'm really new to working on small motors, so please shed some light onto why this is happening here if you can.

  2. crassius

    crassius Well-Known Member

    doctor, my arm hurts when I do this - - - don't do that
    my bike runs bad after changing carb - - -
  3. butre

    butre Well-Known Member

    rejet. if you don't know that you don't have much business swapping carbs
  4. Slogger

    Slogger Member

    The top cap has a lever that holds the spring choke on.
    I have to fiddle with it every time I take it off, to get it in so it works right, holding the choke on till you give it full throttle.
    If you don't live in the mountains, a 66 or 68 dellorto 5mm jet will probably fix you up. These carbs run terrible if the jetting isn't just right. $3 well spent.
    The RT types won't get you more top speed, the NT is better for that. It's simpler and just feeds more gas at full throttle, I guess. On mine the NT was faster but the RT runs perfect, pulls off idle and runs pretty smooth at slower cruising speeds. The NT would spit and sputter off idle and mid range.
    Hope you get er fixed.
  5. imacf90

    imacf90 New Member

    this is really helpful. thanks a lot man. i ordered jets. cant wait to get it running smoothly. i guess i could do some other things to increase the speed, though.
  6. Slogger

    Slogger Member

    Don't mention it. ;)
    The carb I got ran very rich and wasn't any fun til I got the jetting sorted out. I love it now.
    Get a better spark plug and wire, if you haven't already. I like the NGKs but any of them are better than the kit plugs. It's best to wait til after it's broken in before trying to hop it all up for speed. Let it settle in, seat the rings and get it running well. Then you'll see better results trying to hop it up. My engine is still pretty lame for top end, but it is pulling hard at lower RPM and runs pretty smooth.
    I don't go for speed, just smooth running and a nice cruise.
    Good luck!
  7. Fabian

    Fabian Well-Known Member

    There is nothing wrong with the standard NT carburettor once it is jetted correctly. You will not gain any more power when changing to a different carburettor with the same venturi diameter.