Engine Trouble 4 stroking through all rpm's

Discussion in '2-Stroke Engines' started by BennyHam, Feb 4, 2014.

  1. BennyHam

    BennyHam New Member

    I just recently put a kit on my bicycle and im really enjoying it as its my first.
    At the moment it has about 50 miles on it and has been four stroking for about 25 miles. I am using a good oil, started at a 16-1 mix and it was going fine until it started four stroking. so what i have tried is...
    I added an inline filter
    i leaned out the mix and tried, then added more oil and tried again
    i have changed plug NGK B6HS
    tried different setting's on the slide needle
    taken the air filter off for a test
    turned off fuel flow
    and changed the idle screw setting

    the bike is running okay under acceleration and load until it reaches a steady pace then begins for stroking also seems to have a lower top speed and kind of bogs down at WOT.
    checked the plug after a few 20-30 min rides and it was black and wet. i want to lean out the mix but 24-1 left the plug kinda white.

    engine is an unknown brand 48cc slant head.
    air temperature for most rides has been around 4-10 degrees celcius and altitude is around sea level but 50 miles from the coast.
    bike never needed choke to start, choke would only smother it.

    So with all that said can anyone help me?????
    do i have a problem or is this just a break in problem that will go away????
    only thing i haven't tried is a smaller main fet in the carb (NT carb), tempted to put some fine wire in it just to test tomorrow.
    Please guy's all help will be very much appreciated

  2. crassius

    crassius Well-Known Member

    I'd lower the needle for a while and wait till it hits about 200 miles to seat the rings before trying any other tuning.
  3. Fabian

    Fabian Well-Known Member

    Installing a Walbro style diaphragm carburettor will allow easy adjustment of the air/fuel ratio; allowing quick tuning to the point of perfection.
  4. where can you buy one of those?
  5. Fabian

    Fabian Well-Known Member

  6. Purple Haze

    Purple Haze Active Member

    These NT carbs come stock with a #70 jet size. They jet them rich at the factory so they'll start easily and run, but they are too rich to run optimally. I'm sure you can find jets easily in Europe, as these carbs take a 5mm Dellorto jet. I'd start with a #66. I'm at 900 ft above sea level, and mine runs great with a #64 and the needle set at second groove from the top.
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