Cannot get Carburetor Dialed In...

Discussion in '2-Stroke Engines' started by flashstar, Oct 13, 2010.

  1. flashstar

    flashstar Member

    Adjusting the stock NT carburetor on my 2 stroke 70 cc Thatsdax engine has been one of the most frustrating experiences. When I was using the stock exhaust, I downsized the jet from the stock .70 mm size to a .66 mm jet. I picked up a few mph and on acceleration I was 2 stroking more.

    Recently however, I added an expansion chamber. This caused my engine to run really rich with the .66 mm jet. Unburnt oil sludge was actually dripping out of the exhaust. I then installed a .64 mm jet and my plug went from dark black and wet to a drier black color. Oil is still dripping out of the exhaust, but not as badly now lol.

    I have my e-clip on the highest setting so while accelerating, my engine 2 strokes consistently. However, once I reach cruising speed and load is taken off of the engine, it starts to 4 stroke constantly.

    Should I downsize again to a .62 mm jet on move my e-clip down a notch or two? It seems like this might be on the small side for a 70cc engine!


  2. a/c man

    a/c man Member

    Tell us what ratio you are mixing your gas to 2 stroke oil.
    Also what type of oil are you burning?
  3. HeadSmess

    HeadSmess Well-Known Member

    mmmm, id be halving your oil consumption...

    and... cruising speed, no load... i take it your rolling off the throttle as well? or is that still WOT? cus um... if its wot, its still a tad rich, if youre rolling off, its just normal....
  4. flashstar

    flashstar Member

    My ratio of gas to oil is 32:1 with regular valvoline 2 stroke air-cooled oil.

    At cruising speed, I am letting off of the throttle because my engine vibrates so much that it feels like it's going to break apart! Note that I haven't balanced my crank shaft. My engine 4 strokes when I'm cruising at 1/3 throttle.

    When accelerating or climbing hills, my engine 2 strokes pretty consistently. I guess that this is normal?

  5. GearNut

    GearNut Active Member

    32:1 is good, Valvoline is not.
    As for your fuel mixture headache, the taper of the needle may be affecting your ability to properly tune the beast. Try a different, less tapered, thicker needle before going to a smaller jet size.