Carby when a 2 stroke 4 strokes, is it too rich?

Discussion in '2-Stroke Engines' started by motorpsycho, Aug 10, 2010.

  1. motorpsycho

    motorpsycho Active Member

    my engine (66 c.c. h.t. 2 stroke) runs great low-mid rpms.
    but when it gets into the higher rpms, it starts to 4 stroke.
    is this because the main jet in the carb is too rich?
    4 stroking is when there is too much gas and not enough air right?
    i know that adjusting the clip on the carb needle will only help at idle-mid range...not at wide open throttle.
    I have the clip set to the second notch down from the top right now.
    when i got it, the clip was set in the center notch, and it seemed too rich at that point, so i went up one notch with the clip which helped it a lot in the low-mid range rpms
    this is a new engine, that maybe has 40-45 minutes of run time on it. i have been taking it easy and not going more than 1/2 throttle in short bursts. but today i went wide open for a few seconds to see how it would run, and i got the 4 stroking.
    also, i am running a 16:1 gas oil mix for the break in, so could the oil content have something to do with this?

  2. GearNut

    GearNut Active Member

  3. Whizzerd

    Whizzerd Member

    Have you ditched the stock plug and plugwire yet? Upgrading those two items make the HT run like a different engine. And since you're not pushing the engine, try a 20:1 fuel mix. 4 cycling is caused by a rich mixture in most cases. But the bottom line is the engine is not firing on each compression stroke.
  4. motorpsycho

    motorpsycho Active Member

    yes, i have upgraded to the ngk b6hs plug, and tossed the stock plug wire. I made a new plug wire from an accell 8 mm superstock wire with an automotive rubber boot.
    I went with 16:1 because that's what was reccomended in my instruction information.
    I also have another bike with a 49 cc h.t. on it that i built last year. i started right off running 32:1 gas/oil mix, and never really broke that engine in according to the instruction book. That engine runs strong and does not 4 stroke. it has an expansion chamber and modified h.t. muffler on it. my new bike has a long straight pipe with a modified h.t. muffler on it. oh, i am also running synthetic 2 stroke oil in both of my bikes.
    i think my first step is to change my fuel-oil ratio to 20:1 or 24:1, and that might help the problem.
    I mean, the engine runs like a top and has plenty of power, it's just that 4 stroking thing that i hate and i am still not sure if that has to do with the fuel/oil ratio or if it is the main jet. with the needle clip set to the 2nd notch from the top, my spark plug is a gray color. with the clip set to the middle notch, my plug is a tan color. both of these results came after running the engine at 1/2 throttle so the jet needle is still in play. so i left the clip in the center notch. i know that the plug color may change after running it at w.o.t. but i'll have to wait to see how that goes when i get a better mix of fuel-oil in it.
    i know that these carbs normally run rich because of the main jet that comes in the carbs.
    i think once i've ran it for awhile i might have solder the jet closed and re-drill it to make it a tad leaner, i'm not sure yet.
    I just have to get a set of drill bits that are small enough to do it.
  5. GearNut

    GearNut Active Member

    Look at electronic do it your self stores or finer hobby stores for the wire drill bits and a pin vice.
    The pin vice is basically a hand drill that you spin with your fingertips.
    It is usually sold with an assortment of wire drills as a kit.
    Radio Shack used to sell them , but they have regressed in the last 15 years or so.
    I do not know if they still carry them.
  6. machiasmort

    machiasmort Active Member

    As much as I hate to give them credit for anything, Harbor frieght sells drill bits for dremels that are perfect.
  7. AussieSteve

    AussieSteve Active Member

    Nothing wrong with 16:1 for run-in. My kit instructions said the same and I stuck to it. After run-in, I changed to 20:1, again as per the instructions. I've never had a problem with a fouling plug.
    If you reduce the amount of oil in the mix, the fuel/air mixture will be slightly richer and exacerbate the problem.
    An alternative to jet drilling is to buy a ready-made one. Sick Bike Parts sell them.
  8. motorpsycho

    motorpsycho Active Member

    i will have to wait and see how it runs after i run this tank of 16:1 through it.
    once i get the gas/oil mix down to 32:1 or whatever it needs, i will have to see how it runs at that point.
    from there i will pull the carb if needed and see what size the main jet is (i am assuming it's a 70 because most are). if it's too rich at w.o.t. still i will probably drop down to a 68 jet IF sbp sells a 68 jet.