Engine Trouble Tryed everything bike is still unpredictable

Discussion in '2-Stroke Engines' started by mpp313, Feb 4, 2013.

  1. mpp313

    mpp313 New Member

    Over the last few days I have searched the forums and have done everything that was suggested. Heres the story, I built this bike a few months ago. It ran fantastic for the first few weeks, pulled me around at 35mph and I weigh 200. Than it slowly started running worse and worse. I have changed out the spark plug (was black and covered in oil), disasembled and cleaned every part of this terrible CNS carb (one with the sealed mixture screw). Changed out every gasket. Adjusted the clutch. Checked for air leaks. Checked all electrical connections. After all that it seemed to be running great. The motor was really responsive. I go to take it for a ride and it boggs itself down and begins to shake. I left it idling on the back porch while I went to the garage to get a jack stand. I come back to the bike and it is revving itself to death. Smoke pouring off the motor and exhaust. I checked the throttle cable it was fine. I fired it back up after letting it cool for a minute and it idled a little high. So I gave the screw an 1/8th of a turn and it fell on its face. I am at my witts end with this bike. Please any suggestions would be a great help. I know Its probably the carb at fault. But I just don't see how they can sell you a product that absolutely doesn't work. Thanks for your time!

  2. Anton

    Anton Administrator Staff Member

    Like you said it sounds like the carb is at fault. If not maybe an air leak around the intake sucking in too much air.

    Can you give us a better description of what exactly is happening? Basically your saying it starts but then bogs down and dies when you try to ride it?
  3. jaguar

    jaguar Well-Known Member

    It's an air leak at one of these places:
    carb mounting
    intake manifold mounting
    crank seals

    the black spark plug indicates it is jetted too rich (although the air leak causes it to run too lean at idle)
  4. BigBlue

    BigBlue Active Member

    Welcome to the world of Happy Time Engine - having a Happy Time yet? They don't work out of the box - you have to properly setup the engine to get it to run.

    Might want to consider buying an NT carb. What is your fuel/oil ratio? Black covered with oil indicates that your mixture might not be right. If you've already ran it for weeks, no need for a heavy oil mixture. 32:1 is good.

    Good Luck,

    AKA: BigBlue
  5. geebt48cc

    geebt48cc Member

    MPP, understand your pain with CNS! Tell ya what, if you want a good carb with reputable performance, go with That'sDax clone of the Dellorto. $30 bucks, and your out the door with RT carb and filter.
  6. motorpsycho

    motorpsycho Active Member

    whenever an engine idles fine and then revs high by itself, it normally means that you have an air leak, it's running out of fuel in the float bowl, or the throttle slide (or cable) is stuck. the cns carbs are junk in my opinion.
    if your plug was wet and oily, the air-fuel mixture is too rich and you might need to put a leaner jet in the carb.
    but, if you're running an oil-fuel ratio (such as 16:1) you have too much oil in the gas.
    if you're running the fuel -oil ratio at 32:1 or so, you're plug should not be covered with oil.
  7. geebt48cc

    geebt48cc Member

    VERY TRUE!~ ..............Waste of your time on CNS!!! Really, if you continue to try to set that CNS up, you'll end up trashing the whole idea of MB'ing fun. Even if you do find a air leak, toss CNS stuff in trash!!!!!
  8. Fabian

    Fabian Well-Known Member

    Nothing like the good old NT for a simple float style carburettor. It's not perfect but it works well when correctly jetted.
  9. joshua97

    joshua97 Member

    if its that bad get a ned motor off ebay, cheaper than wasting time tryna fix?