66cc runs good under load But 4 strokes on No load

Discussion in '2-Stroke Engines' started by ToyTruck, Jun 24, 2013.

  1. ToyTruck

    ToyTruck Member

    As the title says ... Is this normal or do I need some more tuning .

    66cc , cns carb , rock solid reed valve , standard Cdi

    Normal riding it pulls hard to 1/2 or 3/4
    Then under No load ie flat road it 4 strokes Bad
    But if it is a hill climb , it will run fine WOT and keep running fine as long as there is heavy load ???

    Am I running as good as it gets or....
    Main jet too big ?
    Timing wrong?
    Is it possible that the colder weather is just playing tricks on my tune ???

  2. MusiCALpuLLtoy

    MusiCALpuLLtoy New Member

    its rich. timing???
  3. joshua97

    joshua97 Member

    it 4 strokes? what do u mean by that?
  4. HeadSmess

    HeadSmess Well-Known Member

    yep, sounds pretty normal for a rich mixture.

    "4 stroking" where a two stroke fires on every second stroke due to being too rich. instead of sounding nice and buzzy, it sounds like the chokes been pulled and like...a 4stroke! sort of...
    joshua97 likes this.
  5. crassius

    crassius Well-Known Member

    these are sensitive to temp - takes about 4 miles to get stable, but cold weather can lengthen that

    what you describe doesn't sound horrible, but you could try to lean it out a bit with float height or main jet - remember, too rich is disappointing, too lean is dangerous
  6. ToyTruck

    ToyTruck Member

    The most recent Mod I have done to the motor was drilling out the Main Jet ....
    It just had me a bit baffled as to how it runs perfect under full load then terrible unloaded .

    I will solder and re drill smaller , so it's not a big problem.
    I just wasn't sure if a bit of timing adjust could cure it

    It is definitely too rich , to the point that it actually floods.

    Thanks for the help!
  7. Purple Haze

    Purple Haze Active Member

    Your best bet is to toss that CNS piece of crap, and get a real carb. The "speed" carb is the best low cost carb, available from many sources. Thats Dax sells a chinese-made Dellortto clone that i've heard good things about. But those CNS junkers are a complete waste of time, unless you like constantly tinkering.
  8. ToyTruck

    ToyTruck Member

    Haha I figured the CNS hate would show up soon lol

    The Carby has been fine for me and the only thing that has made it run bad has been me drilling out the main jet ....
    The only reason I posted my question is that it will be a few days before I can tinker with it again and I wanted input to see if I could tune it by timing to cure it or just re-jet .

    I can only assume that , it runs good under load because there is either les vacuum thru the Carby or there might be a slightly different Spark timing from the Standard Cdi at the lower full load rpm ???

    Either way , I will re-jet it a size smaller and see how it goes.
    I would rather buy a Jaguar CDI to try , but they want just as much to ship it as the purchase price ....
  9. Fabian

    Fabian Well-Known Member

  10. keatonx

    keatonx Member

    A 2 stroke will naturally 4 stroke when under light load, ie. engine wound out fully with high gear ratios (less top speed=less top speed load). The extent of this varies from engine to engine (models), but in my experience if it doesn't 4 stroke at all when revved full throttle with the clutch in, it's too lean (it's limiting your torque). However if you can floor it at half-speed and it continues to four stroke up until max speed, then your too rich (assuming your gearing isn't modified for towing cars lol).
    However if you don't four stroke at max speed you don't need to worry, As long as it does with the clutch in. This is actually a good sign, it means you have gearing that makes the most of your engines available torque- for a better top speed

    This is my high tech tuning procedure:jester:
  11. Fabian

    Fabian Well-Known Member

    My experience with these engines is that maximum torque is produced when the air/fuel ratio is on the rich side of the air/fuel ratio for maximum power.

    My experience has also shown that these engines (the 66cc versions) are capable of producing surprisingly good torque (jetted on the rich side) with a standard exhaust system that has had the internal muffler pipe cut off about 2 inches from the base of the end cap.

    The extra torque can be used to propel the bike at acceptable speeds using lower rpm, which gives much less vibration and noise, not to mention a much nicer riding experience, than revving the rings out of the engine all the time.
    The use of lower rpms (3,200 - 4,200) has a side bonus of making the engine last significantly longer and with greater reliability.
  12. keatonx

    keatonx Member

    It's been proven, slightly rich of a stoichiometric (I think that's how its spelled lol) (14.7:1; the air fuel ratio where the engine revs the highest) ratio gives the best overall power. Emissions and fuel economy's a different story tho::grin5: